Ms access tutorials

Microsoft Access Tutorials: Table of Contents
1. Introduction to Microsoft Access 2. Tables
1.1 Introduction: What is Access? 1 2.1 Introduction: The importance of good table
1.1.1 The many faces of Access 1 design 1
1.1.2 What is in an Access database file? 3 2.2 Learning objectives 1
1.2 Learning objectives 3 2.3 Tutorial exercises 1
1.3 Tutorial exercises 4 2.3.1 Datasheet basics 2
1.3.1 Starting Access 4 2.3.2 Creating a new table 2
1.3.2 Creating a new database 4 2.3.3 Specifying the primary key 7
1.3.3 Opening an existing database 6 2.3.4 Setting field properties 7
1.3.4 Importing data from other applications 6 2.3.5 Using the input mask wizard 9
1.3.5 Getting help 9 2.4 Discussion 9
1.3.6 Compacting your database 9 2.4.1 Key terminology 9
1.4 Discussion 14 2.4.2 Fields and field properties 13
1.4.1 The database file in Access 14 2.4.2.1 Field names 13
1.4.2 Compacting a database 14 2.4.2.2 Data types 13
1.4.3 Renaming a database 14 2.4.2.3 “Disappearing” numbers in autonumber
1.4.4 Developing applications in Access 15 fields 14
1.4.5 Use of linked tables 16 2.4.2.4 Input masks 15
1.5 Application to the assignment 16 2.4.2.5 Input masks and literal values 16

© Michael Brydon (brydon@unixg.ubc.ca)
Last update: 25-Aug-1997 Home Previous 1 of 8 Next

2.5 Application to the assignment 17 4.3.1 Creating a query 2
4.3.2 Five basic query operations 2
3. Relationships 4.3.2.1 Projection 2
3.1 Introduction: The advantage of using tables 4.3.2.2 Sorting 7
and relationships 1 4.3.2.3 Selection 7
3.1.1 “Normalized” table design 3 4.3.2.4 Complex selection criteria 7
3.2 Learning objectives 4 4.3.2.5 Joining 11
3.3 Tutorial exercises 4 4.3.3 Creating calculated fields 15
3.3.1 Creating relationships between tables 4 4.3.3.1 Refining the calculated field 18
3.3.2 Editing and deleting relationships 7 4.3.3.2 A more complex calculated field 18
3.4 Discussion 7 4.3.4 Errors in queries 20
3.4.1 One-to-many relationships 7 4.4 Discussion 20
3.4.2 Referential integrity 9 4.4.1 Naming conventions for database
3.5 Application to the assignment 10 objects 20
4.4.2 The ampersand (&) operator 21
4. Basic Queries Using QBE 4.4.3 Using queries to populate tables on the
4.1 Introduction: Using queries to get the “many” side of a relationship 22
information you need 1 4.4.4 Non-updatable recordsets 23
4.2 Learning objectives 1 4.5 Application to the assignment 27
4.3 Tutorial exercises 2

Home Previous 2 of 8 Next

5. Basic Queries using SQL 6.3.1.4 Binding an unbound text box to a field 9
5.1 Introduction: The difference between QBE 6.3.2 Creating a single-column form using the
and SQL 1 wizard 11
5.2 Learning objectives 1 6.4 Discussion 14
5.3 Tutorial exercises 1 6.4.1 Columnar versus tabular versus
5.3.1 Basic SQL queries 2 datasheet forms 14
5.3.2 Complex WHERE clauses 4 6.5 Application to the assignment 14
5.3.3 Join queries 4
5.4 Discussion 5 7. Subforms
7.1 Introduction: The advantages of forms
6. Form Fundamentals within forms 1
6.1 Introduction: Using forms as the core of an 7.2 Learning objectives 1
application 1 7.3 Tutorial exercises 1
6.2 Learning objectives 1 7.3.1 Creating the main form 3
6.3 Tutorial exercises 2 7.3.2 Creating the subform 3
6.3.1 Creating a form from scratch 2 7.3.3 Linking the main form and subform 3
6.3.1.1 Adding bound text boxes 2 7.3.4 Linking forms and subforms manually 9
6.3.1.2 Using a field’s properties to protect its 7.3.5 Non-synchronized forms 13
contents 6 7.3.6 Aesthetic refinements 13
6.3.1.3 Adding an unbound text box 6 7.3.6.1 Changing the form’s caption 13


7.3.6.2 Eliminating unwanted scroll bars and 8.4.1 Why you should never use a combo box
navigation buttons 13 for a non-concatenated key. 19
7.4 Application to the assignment 16 8.4.2 Controls and widgets 21
8.5 Application to the assignment 22
8. Combo Box Controls
8.1 Introduction: What is a combo box? 1 9. Advanced Forms
8.2 Learning objectives 2 9.1 Introduction: Using calculated controls on
8.3 Tutorial exercises 2 forms 1
8.3.1 Creating a bound combo box 2 9.2 Learning objectives 1
8.3.2 Filling in the combo box properties 5 9.3 Tutorial exercises 1
8.3.3 A combo box based on another table or 9.3.1 Creating calculated controls on forms 1
query 6 9.3.2 Showing a total on the main form 2
8.3.3.1 Showing more than one field in the 9.3.2.1 Calculating the aggregate function on
combo box 9 the subform 5
8.3.3.2 Hiding the key field 12 9.3.2.2 Hiding the text box on the subform 9
8.3.3.3 Changing the order of items in the 9.4 Discussion 9
combo box 14 9.5 Application to the assignment 11
8.3.4 Changing a form’s tab order 18
8.4 Discussion 19


10. Parameter Queries 11.3.2 Using an update query to rollback
10.1 Introduction: Dynamic queries using changes 3
parameters 1 11.3.3 Using an update query to make
10.2 Learning objectives 1 selective changes 8
10.3 Tutorial exercises 2 11.3.4 Rolling back the changes 9
10.3.1 Simple parameter queries 2 11.3.5 Attaching action queries to buttons 9
10.3.2 Using parameters to generate prompts 11.4 Application to the assignment 11
4 11.4.1 Rolling back your master tables 11
10.3.3 Values on forms as parameters 4 11.4.2 Processing transactions 16
12. An Introduction to Visual Basic
11. Action Queries 12.1 Introduction: Learning the basics of
11.1 Introduction: Queries that change data 1 programming 1
11.1.1 What is an action query? 1 12.1.1 Interacting with the interpreter 1
11.1.2 Why use action queries? 1 12.2 Learning objectives 2
11.3 Tutorial exercises 3 12.3.1 Invoking the interpreter 2
11.3.1 Using a make-table query to create a 12.3.2 Basic programming constructs 3
backup 3 12.3.2.1 Statements 3
12.3.2.2 Variables and assignment 3


12.3.2.3 Predefined functions 4 13.1.2 The Access macro language 2
12.3.2.4 Remark statements 5 13.1.3 The trigger design cycle 3
12.3.3 Creating a module 6 13.2 Learning objectives 3
12.3.4 Creating subroutines with looping and 13.3 Tutorial exercises 4
branching 7 13.3.1 The basics of the macro editor 4
12.3.4.1 Declaring variables 7 13.3.2 Attaching the macro to the event 5
12.3.4.2 Running the subroutine 9 13.3.3 Creating a check box to display update
12.3.4.3 Conditional branching 9 status information 9
12.3.5 Using the debugger 10 13.3.4 The SetValue command 10
12.3.6 Passing parameters 11 13.3.5 Creating conditional macros 10
12.3.7 Creating the Min() function 13 13.3.5.1 The simplest conditional macro 13
12.4 Discussion 14 13.3.5.2 Refining the conditions 15
12.4.1 Interpreted and compiled languages 14 13.3.5.3 Creating a group of named macros 16
12.5 Application to the assignment 16 13.3.6 Creating switchboards 17
13.3.6.1 Using a macro and manually-created
13. Event-Driven Programming Using buttons 21
Macros 13.3.6.2 Using the button wizard 21
13.1 Introduction: What is event-driven 13.3.7 Using an autoexec macro 21
programming? 1 13.4 Discussion 25
13.1.1 Triggers 2 13.4.1 Event-driven programming versus
conventional programming 25


13.5 Application to the assignment 26 14.5.1 Using a separate table to store system
parameters 20
14. Data Access Objects 14.5.2 Determining outstanding backorders21
14.1 Introduction: What is the DAO hierarchy?1
14.1.1 DAO basics 1 15. Advanced Triggers
14.1.2 Properties and methods 2 15.1 Introduction: Pulling it all together 1
14.1.3 Engines, workspaces, etc. 3 15.2 Learning objectives 1
14.3 Tutorial exercises 5 15.3.1 Using a macro to run VBA code 1
14.3.1 Setting up a database object 5 15.3.1.1 Creating a wrapper 2
14.3.2 Creating a Recordset object 7 15.3.1.2 Using the RunCode action 2
14.3.3 Using a Recordset object 8 15.3.2 Using activity information to determine
14.3.4 Using the FindFirst method 10 the number of credits 4
14.3.5 The DLookUp() function 12 15.3.2.1 Scenario 4
14.3.5.1 Using DLookUp() in queries 15 15.3.2.2 Designing the trigger 6
14.3.5.2 Understanding the WHERE clause 15 15.3.2.3 Preliminary activities 8
14.4 Discussion 17 15.3.2.4 Looking up the default value 8
14.4.1 VBA versus SQL 17 15.3.2.5 Changing the Record Source of the
14.4.2 Procedural versus Declarative 19 form 10
14.5 Application to the assignment 20 15.3.2.6 Creating the SetValue macro 11


15.3.2.7 Attaching a procedure to the After 15.4.3 Understanding the
Update event 11 UpdateBackOrders() function 24
15.3.3 Use an unbound combo box to 15.4.4 Annotated source code for the
automate search 12 backorders shortcut module. 27
15.3.3.1 Manual search in Access 12 15.4.4.1 The UpdateBackOrders() function
15.3.3.2 Preliminaries 13 27
15.3.3.3 Creating the unbound combo box 13 15.4.4.2 Explanation of the
15.3.3.4 Automating the search procedure using UpdateBackOrders() function 27
a macro 16 15.4.4.3 The BackOrderItem() subroutine30
15.3.4 Using Visual Basic code instead of a 15.4.4.4 Explanation of the BackOrderItem()
macro 19 subroutine 31
15.4.1 Triggers to help the user 20
15.4.2 Updating the BackOrders table 22
15.4.2.1 Create the pqryItemsToBackOrder
query 23
15.4.2.2 Import the shortcut function 23
15.4.2.3 Use the function in your application 24
15.4.2.4 Modifying the UpdateBackOrders()
function 24


Access Tutorial 1: Introduction to Microsoft Access
The purpose of these tutorials is not to teach you • Microsoft SQL Server
Microsoft Access, but rather to teach you some • IBM DB2
generic information systems concepts and skills • Informix
using Access. Of course, as a side effect, you will Well-know PC-based (“desktop”) relational DBMSes
learn a great deal about the software—enough to include
write your own useful applications. However, keep in • Microsoft Access
mind that Access is an enormously complex, nearly- • Microsoft FoxPro
industrial-strength software development environ- • Borland dBase
ment. The material here only scrapes the surface of
Access development and database programming. 1.1.1 The many faces of Access
Microsoft generally likes to incorporate as many fea-
1.1 Introduction: What is Access? tures as possible into its products. For example, the
Microsoft Access is a relational database manage- Access package contains the following elements:
ment system (DBMS). At the most basic level, a • a relational database system that supports two
DBMS is a program that facilitates the storage and industry standard query languages: Structured
retrieval of structured information on a computer’s Query Language (SQL) and Query By Example
hard drive. Examples of well-know industrial-strength (QBE);
relational DBMSes include
• Oracle

Last update: 24-Aug-1997 Home Previous 1 o f 17 Next

1. Introduction to Microsoft Access Introduction: What is Access?

• a full-featured procedural programming lan- • the procedural programming personality expects
guage—essentially a subset of Visual Basic, you to view your application as commands to be
• a simplified procedural macro language unique executed sequentially;
to Access; • the object-oriented personality expects you to
• a rapid application development environment view your application as objects which encapsu-
complete with visual form and report develop- late state and behavior information.
ment tools; Microsoft makes no effort to provide an overall logi-
• a sprinkling of objected-oriented extensions; cal integration of these personalities (indeed, it is
and, unlikely that such an integration is possible). Instead,
• various wizards and builders to make develop- it is up to you as a developer to pick and choose the
ment easier. best approach to implementing your application.
For new users, these “multiple personalities” can be Since there are often several vastly different ways to
a source of enormous frustration. The problem is implement a particular feature in Access, recogniz-
that each personality is based on a different set of ing the different personalities and exploiting the best
assumptions and a different view of computing. For features (and avoiding the pitfalls) of each are impor-
instance, tant skills for Access developers.
• the relational database personality expects you
The advantage of these multiple personalities is that
to view your application as sets of data;
it is possible to use Access to learn about an enor-
mous range of information systems concepts without

Home Previous 2 o f 17 Next

1. Introduction to Microsoft Access Learning objectives

having to interact with a large number of “single-per- • macros and Visual Basic programs for extending
sonality” tools, for example: the functionality of database applications.
• Oracle for relational databases All these database objects are stored in a single file
• PowerBuilder for rapid applications development, named <filename>.mdb. When you are running
• SmallTalk for object-oriented programming. Access, a temporary “locking” file named <file-
Keep this advantage in mind as we switch back and name>.ldb is also created. You can safely ignore
forth between personalities and different computing the *.ldb file; everything of value is in the *.mdb file.
paradigms.
1.2 Learning objectives
1.1.2 What is in an Access database
file?
How do I get started?

Although the term “database” typically refers to a col-
How do I determine the version I am using?

lection of related data tables, an Access database How do I create or edit a database object?
includes more than just data. In addition to tables, an What is the database window and what does
Access database file contains several different types it contain?
of database objects: How do I import an Excel spreadsheet?

• saved queries for organizing data,
• forms for interacting with the data on screen, How do I delete or rename database objects?
• reports for printing results,


1. Introduction to Microsoft Access Tutorial exercises

How do I get help from the on-line help Access from the main menu to see which version
system? you are using.
How do I compact a database to save space?
All the screen shots in these tutorials are
taken from Access version 7.0 (released as
1.3 Tutorial exercises part of Office 95). Although there are some
In this tutorial, you will start by creating a new data- important differences between version 2.0
base file. and version 7.0, the concepts covered here
are the same for both. Version 8.0 (released
1.3.1 Starting Access as part of Office 97) is only slightly different
• To start Access, you double click the Access icon from version 7.0.
( for version 8.0 and 7.0 or for version
2.0) from within Microsoft Windows.
If you are working in the Commerce PC Lab, you will
Whenever the instructions given in the tutorial
differ significantly from version 7.0, a warning
box such as this is used.
be working with Access version 2.0. If you are work-
ing at home, you will able be to tell what version you
1.3.2 Creating a new database
are using by watching the screen “splash” as the pro-
gram loads. Alternatively, select Help About • Follow the directions in Figure 1.1 to create a
new database file called myfile.mdb.



FIGURE 1.1: Select the name and location of your new (empty) database.

New from thedatabase by selecting File the
Create a new
main menu or by clicking
“new database” button on the tool bar.

Note thata you are limited to 8-letter names in
Type in new database name and press Enter.

version 2.0.



• Examine the main features of the database win-
dow—including the tabs for viewing the different If you are using version 8.0, you can use
either univ0_v2.mdb or univ0_v7.mdb for
database objects—as shown in Figure 1.2. the tutorials. When you open the file, Access
will ask you if you want to convert it to version
1.3.3 Opening an existing database 8.0. Select yes and provide a new name for
Since an empty database file is not particularly inter- the converted file (e.g., univ0_v8.mdb)
esting, you are provided with an existing database
• Open the univ0_vx.mdb file and examine the
file containing information about university courses.
contents of the Sections table, as shown in
For the remainder of this tutorial, we will use a file
Figure 1.3.
called univ0_v7.mdb, which is available from the
tutorial’s Internet site.
1.3.4 Importing data from other

If you are using version 2.0, you will need to applications
use the univ0_v2.mdb database instead. Access makes it easy to import data from other
Although you can open a version 2.0 data- applications. In this section, you will create a new
base with version 7.0, you cannot open a ver- table using data from an Excel spreadsheet.
sion 7.0 database with version 2.0. Importing • Select File Get External Data Import from the
and exporting across versions is possible, main menu and import the depts.xls spread-
however.



FIGURE 1.2: The database window contains all the database objects for a particular application.

The database window is always
available from the Window menu.
Tables —
contain data
in rows and Modules —
columns. contain Visual
Basic
procedures and
functions.
Queries — allow the
information in Macros — are sets of high-
tables to be sorted, level commands that can be
filtered, and shown used to process data and
in different ways. perform repetitive tasks.
Forms — are for Reports —are
displaying for organizing
information on and printing
the screen. information.



FIGURE 1.3: Open the univ0_vx.mdb file for the version of Access that you are using and then
open the Sections table

from the mainOpen Database
Select File
menu.
You can open a
database object for
viewing, for
modification, or
create a new object.

correctthe and
Select
file
open the
Sections
table.



sheet as a new table called Departments (see 1.3.5 Getting help
Figure 1.4). A recent trend in commercial software (especially
from Microsoft) is a reliance on on-line help and doc-
In version 2.0, the menu structure is slightly
different. As such, you must use File Import.
umentation in lieu of printed manuals. As a conse-
quence, a good understanding of how to use the on-
• Use the import wizard specify the basic import line help system is essential for learning any new
parameters. You should accept all the defaults software. In this section, you will use Access’ on-line
provided by the wizard except for those shown in help system to tell you how to compact a database.
Figure 1.5. • Press F1 to invoke the on-line help system. Find
• Double click the Departments table to ensure it information on compacting a database, as shown
was imported correctly. in Figure 1.6.
• Familiarize yourself with the basic elements of
If you make a mistake, you can rename or the help window as shown in Figure 1.7.
delete a table (or any database object in the
database window) by selecting it and right- 1.3.6 Compacting your database
clicking (pressing the right mouse button • Follow the directions provided by the on-line help
once). window shown in Figure 1.7 to compact your
database.



FIGURE 1.4: Import the dept.xls spreadsheet as a table called Departments.

Double-click depts.xls.

ImportFile the from the main menu
Select
from
Get External Data

and move the directory containing the
file you want to import. with that extension *.xls (files
Select files of type
will show in
the file window).



FIGURE 1.5: Use the spreadsheet import wizard to import the Excel file.

column headings option so
Select the first row contains

that the column headings in the
spreadsheet are not interpreted
as data.

about primary keystalked
Since we have not
yet,
select no primary key.



lettersin the first few
Type FIGURE 1.6: Use the help system to find
of the topic you information on a specific topic
are looking for.

the list the best match from
Select
(i.e., “compacting
databases”) and double-
click to get a list of topics.

Double click the most
promising entry in this list
to get the actual help topic.

The Index is the best place to For most students, the help
start when you are looking for a system in Access version
specific topic. If you need more 2.0 is easier to navigate.
structured information or are Use the “cue cards” in
looking for an overview, use the version 2.0 to get step-by-
Contents tab. step instructions for many
operations.



FIGURE 1.7: Follow the instructions provided by help to compact your database

Minimize (rather than close) help
when you are working so that you can
use the Back button to return to
previously visited topics without
repeating the search.

Press help topics to return to the
index.

Words underlined with a dashed line
provide important definitions.


1. Introduction to Microsoft Access Discussion

1.4 Discussion 1.4.2 Compacting a database
As the help system points out, Access database files
1.4.1 The database file in Access can become highly fragmented and grow to become
The term “database” means different things depend- much larger than you might expect given the amount
ing on the DBMS used. For example in dBase IV, a of data they contain (e.g., multiple megabytes for a
database is a file (filename.dbf) containing a handful of records). Compacting the database from
single table. Forms and reports are also stored as time to time eliminates fragmentation and can dra-
individual files with different extensions. The net matically reduce the disk space requirement of your
result is a clutter of files. database.
In contrast, an Oracle database has virtually no rela-
tionship to individual files or individual projects. For 1.4.3 Renaming a database
instance, a database may contain many tables from It is often the case that you are working with a data-
different projects/applications and may also be base and want to save it under a different name or
stored split into one or more files (perhaps on differ- save it on to a different disk drive. However, one
ent machines). command on the File menu that is conspicuous by its
Access strikes a convenient balance—all the absence is Save As.
“objects” (tables, queries, forms, reports, etc.) for a However, when compacting your database, Access
single project/application are stored in a single file. asks for the name and destination of the compacted
file. As a result, the compact database utility can be


1. Introduction to Microsoft Access Discussion

used as a substitute for the Save As command. This mended sequence for prototyping using Access is
is especially useful in situations in which you cannot the following:
use the operating system to rename a file (e.g., 1. Model the information of interest in terms of enti-
when you do not have access to the Windows file ties and relationships between the entities (this is
manager). covered in the lecture portion of the course).
2. Create a table for each entity (Tutorial 2).
1.4.4 Developing applications in Access 3. Specify the relationships between the tables
In general, there are two basic approaches to devel- (Tutorial 3).
oping information systems: 4. Organize the information in your tables using
• in-depth systems analysis, design, and imple- queries (Tutorial 4, Tutorial 5, Tutorial 10)
mentation, 5. Create forms and reports to support input and
• rapid prototyping (in which analysis, design, and output transactions (Tutorial 6, Tutorial 7).
implementation are done iteratively) 6. Enhance you forms with input controls
Access provides a number of features (such as (Tutorial 8)
graphical design tools, wizards, and a high-level 7. Create action queries (Tutorial 11), macros
macro language) that facilitate rapid prototyping. (Tutorial 13), or Visual Basic programs
Since you are going to build a small system and (Tutorial 12, Tutorial 14) to perform the transac-
since time is limited, you will use a rapid prototyping tion processing functions of the application.
approach to build your application. The recom-


1. Introduction to Microsoft Access Application to the assignment

8. Create “triggers” (procedures attached to events) machine, update the links to the data file, and the
to automate certain repetitive tasks (Tutorial 15). upgrade is done.

1.4.5 Use of linked tables Do not used linked tables in the assignment.
The links are dependent on the absolute
Most professional Access developers do not put their
directory structure. As a result, if the directory
tables in the same database file as their queries,
structure on your machine is different from
forms, reports, and so on. The reason for this is sim-
that on the marker’s machine, the marker will
ple: keep the application’s data and interface sepa-
not be able to use your application without
rate.
first updating the links (a time consuming pro-
Access allows you to use the “linked table” feature to cess for a large number of assignments).
link two database files: one containing all the tables
(“data”) and another containing all the interface and 1.5 Application to the assignment
logic elements of the application (“interface”). The
After completing this tutorial you should be ready to
linked tables from the data file show up in the inter-
face file with little arrows (indicating that they are not create the database file that you will use for the
remainder of the course.
actually stored in the interface file).
1. Create an empty database file called your
In this way, you can modify or update the interface
file without affecting the actual data in any way. You groupID.mdb. Remember that your group
number consists of eight digits.
just copy the new interface file over to the user’s


1. Introduction to Microsoft Access Application to the assignment

2. Import the inventor.xls spreadsheet as your
Products table.
3. Use the compact utility to make a backup copy of
your database (use a different name such as
backup.mdb).


Access Tutorial 2: Tables
2.1 Introduction: The importance 2.2 Learning objectives
of good table design How do I enter and edit data in the datasheet
Tables are where data in a database is stored; con- view of a table?
sequently, tables form the core of any database How do I create a new table?
application. In addition to basic data, Access permits
a large amount of domain knowledge (such as cap-
How do I set the primary key for a table?

tions, default values, constraints, etc.) to be stored at How do I specify field properties such as the
the table level. input mask and caption?

Extra time spent thinking about table design
Why won’t an autonumber field restart
counting at one?

can result in enormous time savings during
later stages of the project. Non-trivial changes What are the different types of keys?
to tables and relationships become increas-
ingly difficult as the application grows in size 2.3 Tutorial exercises
and complexity. In this tutorial, you will learn to interact with existing
tables and design new tables.


2. Tables Tutorial exercises

2.3.1 Datasheet basics such as lecturers, department heads, departmental
• If you have not already done so, open the secretaries, and so on.
univ0_vx.mdb database file from Tutorial 1. • Return to the database window and create a new
• Open the Departments table. The important table as shown in Figure 2.3.
elements of the datasheet view are shown in • In the table design window shown in Figure 2.4,
Figure 2.1. type in the following information:
• Use the field selectors to adjust the width of the Description
Field name Data type
DeptName field as shown in Figure 2.1. (optional)
• Add the Biology department (BIOL) to the table, EmployeeID Text use employee
as shown in Figure 2.2. S.I.N.
• Delete the “Basket Weaving” record by clicking FName Text First name
on its record selector and pressing the Delete
LName Text Last name
key.
Phone Text
2.3.2 Creating a new table Salary Currency
In this section you will create and save a very basic
skeleton for table called Employees. This table • Select File Save from the main menu (or press
could be used to keep track of university employees Control-S) and save the table under the name
Employees.



FIGURE 2.1: The datasheet view of the Departments table.

The field names are shown in the “field
selectors” across the top of the columns. the columnDeptName draggingby clicking near
Resize the
border and
column
the border to
the right.
You can temporarily sort the records
in a particular order by right-clicking
any of the field selectors.

The records are shown as rows.

The black triangle indicates the
“current record”.
The asterisk (*) indicates a
The grey boxes are “record selectors”. place holder for a new record.

The “navigation buttons” at the bottom of the window
indicate the current record number and allow you to go
directly to the first, previous, next, last, or new record.



FIGURE 2.2: Adding and saving a record to the table.

of thea “newrecord byfield (marked byDeptCode field
Add new
record”
clicking in the
the asterisk).
It is seldom necessary to
explicitly save new
records (or changes to
existing records) since
Access automatically
saves whenever you
move to another record,
close the table, quit
Access, etc.

data, click on thesave theselector (note the
To permanently
record
change to the

icon changes from a pencil to a triangle).



FIGURE 2.3: Create a new table.

createthenew table. to
Click
a
New button

the table wizard at this point).
Select “design view” (avoid using



FIGURE 2.4: Use the table design window to enter the field properties for the Employees table.

data typesfieldthe five and
Enter the
for
names
fields.

The “description” column allows
you to enter a short comment
about the field (this information
is not processed in any way by
Access).

The “field properties” section
allows you to enter information
about the field and constraints on
the values for the field.



2.3.3 Specifying the primary key
FIGURE 2.6: Set the field properties for the
Tables normally have a primary key that uniquely EmployeeID field.
identifies the records in the table. When you desig-
nate a field as the primary key, Access will not allow
you to enter duplicate values into the field.
• Follow the steps in Figure 2.5 to set the primary
key of the table to EmployeeID.

2.3.4 Setting field properties
In this section, you will specify a number of field
properties for the EmployeeID field, as shown in
Figure 2.6.
• Since we are going to use the employees’ Social
Insurance Number (S.I.N.) to uniquely identify
them, set the Field Size property to 11 characters
(9 for numbers and 2 for separating spaces)
• Set the Input Mask property to the following:
000 000 000;0
• Set the Caption property to Employee ID



FIGURE 2.5: Set the primary key for the Employees table.

fields)on the greythe primary key.field (or
Click
that form
box beside the

To select more than one field for use as the
primary key, hold down the Control key
while clicking on the grey boxes.

select Edit the key-shaped from in the tool bar or
Either click
Primary Key
icon
the menu.


2. Tables Discussion

• Select View Datasheet from the main menu to three small dots ( ) to invoke the input mask
switch to datasheet mode as shown in Figure 2.7. wizard.
Enter your own S.I.N. and observe the effect of • Follow the instructions provided by the wizard as
the input mask and caption on the EmployeeID shown in Figure 2.8.
field. • Press F1 while the cursor is still in the input mask
• Select View Table Design from the main menu property. Scroll down the help window to find the
to return to design mode. meaning of the “0”, “9”, “” and “L” input mask
• Set the field properties for FName and LName symbols.
(note that Length and Caption are the only two
properties that are relevant for these two fields) 2.4 Discussion
2.3.5 Using the input mask wizard 2.4.1 Key terminology
In this section, you will use the input mask wizard to A key is one or more fields that uniquely determine
create a complex input mask for a standard field the identity of the real-world object that the record is
type. You will also use the help system to learn more meant to represent. For example, there is a record in
about the meaning of the symbols used to create the student information system that contains infor-
input masks. mation about you as a student. To ensure that the
• Select the Phone field, move the cursor to the record is associated with you and only you, it con-
input mask property, and click the button with



FIGURE 2.7: Observe the effect of the input mask and caption properties on the behavior of the
EmployeeID field during data entry

numbers intovarious characters and
Try entering
the EmployeeID
field.
If a caption is specified, it replaces the
done to clear the changes to the record.
Press the Escape key when you are

field name in the field selector.
Note that the input mask will not let you
type any characters other than numbers
from 0-9. In addition, the spaces between
the groups of numbers are added
automatically.
Input masks provide a relatively easy way to
avoid certain basic data input errors without
having to write complex error checking
programs. Note, however, that it is possible to
over-constrain a field so that users are unable to
enter legitimate values.



FIGURE 2.8: Use the input mask wizard to create an input mask.

number” from the
Select “phone

list of commonly-
used field types.

The items in this
list depend on the
“international
settings” specified
for Windows (e.g.,
“Zip Code” may
show instead of Since the input mask controls how
“Postal Code”). the information in the field looks, it
is possible to save some disk space
by storing the data without the
edit the 2, youmask
In Step
input
may extras symbols, spaces, etc. For the
size of system we are building,
(e.g., remove the however, this savings is negligible.
area code section).



tains a field called “student number” that is guaran- nated key is made by joining together two or
teed to be unique. more fields. Course numbers at UBC provide a
The advantage of using student number as a key good example of a concatenated key made by
instead of some other field—like “student name”—is joining together two fields: DeptCode and
that there may be more than one person with the CrsNum. For example, department alone cannot
same first and last name. The combination of stu- be the primary key since there are many courses
dent name and address is probably unique (it is in each department (e.g., COMM 335, COMM
improbable that two people with the same name will 391). Similarly, course number cannot be used as
at the same address) but using these two fields as a a key since there are many courses with the
key would be cumbersome. same number in different departments (e.g.,
COMM 335, HIST 335, MATH 335). However,
Since the terminology of keys can be confusing, the
department and course number together form a
important terms are summarized below.
concatenated key (there is only one COMM 335).
1. Primary key — The terms “key” and “primary 3. Foreign key: In a one-to-many relationship, a
key” are often used interchangeably. Since there foreign key is a field (or fields) in the “child”
may be more than one candidate key for an record that uniquely identifies the correct “parent”
application, the designer has to select one: this is record. For example, DeptCode and CrsNum in
the primary key. the Sections table are foreign keys since these
2. Concatenated key: The verb “concatenate” two keys taken together are the primary key of
means to join together in a series. A concate-



the Courses table. Foreign keys are identified in In addition, you can use the comment field in the
Access by creating relationships (see Tutorial 3). table design window to document the meaning of
field names.
2.4.2 Fields and field properties
It is strongly recommended that you avoid all
2.4.2.1 Field names
non-alphanumeric characters whenever you
Access places relatively few restrictions on field name a field or database object. Although
names and thus it is possible to create long, descrip- Access will permit you to use names such as
tive names for your fields. The problem is that you Customer#, non-alphanumeric characters
have to type these field names when building que- (such as #, /, $, %, ~, @, etc.) may cause
ries, macros, and programs. As such, a balance undocumented problems later on.
should be struck between readability and ease of
typing. You are advised to use short-but-descriptive 2.4.2.2 Data types
field names with no spaces. The field's data type tells Access how to handle the
For example, in Section 2.3.2 you created a field information in the field. For instance, if the data type
with name FName. However, you can use the caption is date/time, then Access can perform date/time
property to provide a longer, more descriptive label arithmetic on information stored in the field. If the
such as First name. The net result is a field name same date is stored as text, however, Access treats
that is easy to type when programming and a field it just like any other string of characters. Normally,
caption that is easy to read when the data is viewed.



the choice of data type is straightforward. However, for use as a primary key when no other key is
the following guidelines should be kept in mind: provided or is immediately obvious.
1. Do not use a numeric data type unless you are
Since an autonumber is really Long Integer
going to treat the field as a number (i.e., perform
and since relationships can only be created
mathematical operations on it). For instance, you
between fields with the same data type, it is
might be tempted to store a person's student
important to remember that if an autonumber
number as an integer. However, if the student
is used on the “one” side of a relationship, a
number starts with a zero, then the first digit is
long integer must be used for the “many” side.
dropped and you have to coerce Access into dis-
playing it. Similarly, a UBC course number (e.g., 2.4.2.3 “Disappearing” numbers in
335) might be considered a number; however, autonumber fields
since courses like 439B have to accommodated,
If, during the process of testing your application, you
a numeric data type for the course number field is
add and delete records from a table with an auto-
clearly inappropriate.
number key, you will notice that the deleted keys are
2. Access provides a special data type called Auto
not reclaimed.
Number (Counter in version 2.0). An autonum-
ber/counter is really a number of type Long Inte- For instance, if you add records to your Customer
ger that gets incremented by Access every time table (assuming that CustID is an autonumber), you
a new record is added. As such, it is convenient will have a series of CustID values: 1, 2, 3… If you



later delete customer 1 and 2, you will notice that lutely no difference whether the first customer in your
your list of customers now starts at 3. customers table is CustID = 1 or 534.
Clearly, it would be impossible for Access to renum- 2.4.2.4 Input masks
ber all the customers so the list started at 1. What An input mask is a means of restricting what the user
would happen, for instance, to all the printed
can type into the field. It provides a “template” which
invoices with CustID = 2 on them? Would they refer tells Access what kind of information should be in
to the original customer 2 or the newly renumbered
each space. For example, the input mask LLLL
customer 2? consists of two parts:
The bottom line is this: once a key is 1. The right brace ensures that every character
assigned, it should never be reused, even if the user types is converted into upper case.
the entity to which it is assigned is subse- Thus, if the user types comm, it is automatically
quently deleted. Thus, as far as you are con- converted to COMM.
cerned, there is no way to get your customers 2. The characters LLLL are place holders for letters
table to renumber from CustID = 1. from A to Z with blank spaces not allowed. What
this means is that the user has to type in exactly
Of course, there is a long and complicated way to do four letters. If she types in fewer than four or
it, but since used an autonumber in the first place, types a character that is not within the A to Z
you do not care about the actual value of the key— scope (e.g., , 7, %), Access will display an error
you just want it to be unique. In short, it makes abso- message.



There are a large number of special symbols used The semicolon and zero at the end of this input mask
for the input mask templates. Since the meaning of are important because, as the on-line help system
many of the symbols is not immediately obvious, points out, an input mask value actually consists of
there is no requirement to remember the character three parts (or “arguments”), each separated by a
codes. Instead, simply place the cursor on the input semicolon:
mask property and press F1 to get help. In addition, • the actual template (e.g., 000-0000),
the wizard can be used to provide a basic input mask • a value (0 or 1) that tells Access how to deal with
which can later be modified. literal characters, and
2.4.2.5 Input masks and literal values • the character to use as a place holder (showing
the user how many characters to enter).
To have the input mask automatically insert a char-
When you use a literal character in an input mask,
acter (such as a space or a dash) in a field, use a
slash to indicate that the character following it is a lit- the second argument determines whether the literal
value is simply displayed or displayed and stored in
eral.
the table as part of the data.
For example, to create an input mask for local tele-
For example, if you use the input mask 000-
phone numbers (e.g., 822-6109), you would use the
following template: 000-0000;0 (the dash is a lit- 0000;1, Access will not store the dash with the tele-
phone number. Thus, although the input mask will
eral value and appears automatically as the user
enters the telephone number). always display the number as “822-6109”, the num-
ber is actually stored as “8226109”. By using the


2. Tables Application to the assignment

input mask 000-0000;0, however, you are telling 2.5 Application to the assignment
Access to store the dash with the rest of the data.
You now have the skills necessary to implement your
If you use the wizard to create an input mask, tables.
it asks you a simple question about storing lit- • Create all the tables required for the assignment.
eral values (as shown in Figure 2.8) and fills • Use the autonumber data type (counter in version
in the second argument accordingly. How- 2.0) for your primary keys where appropriate.
ever, if you create the input mask manually, • Specify field properties such as captions, input
you should be aware that by default, Access mask, and defaults where appropriate.
does not store literal values. In other words,
If you create an input mask for ProductID,
the input mask 000-0000 is identical to the
ensure you understand the implications of
input mask 000-0000;1. This has impor-
Section 2.4.2.5.
tant consequences if the field in question is
subject to referential integrity constraints (the • Set the Default property of the OrderDate field
value “822-6109” is not the same as so that the current date is automatically inserted
“8226109”). into the field when a new order is created (hint:
see the Date() function in the on-line help sys-
tem).


2. Tables Application to the assignment

• Do not forget to modify your Products table (the
data types, lengths, and field properties of
imported tables normally need to be fine tuned)
• Populate (enter data into) your master tables. Do
not populate your transaction tables.

For the purpose of the assignment, the term
“transaction” tables refers to tables that con-
tain information about individual transactions
(e.g., Orders, OrderDetails, Ship-
ments, ShipmentDetails). “Master”
tables, in contrast, are tables that either do
not contain information about transactions
(e.g., Customers) or contain only summary
or status information about transactions (e.g.,
BackOrders).


Access Tutorial 3: Relationships
3.1 Introduction: The advantage of 1. Wasted space — Note that for COMM 290, the
using tables and relationships same basic course information is repeated for
every section. Although the amount of disk space
A common mistake made by inexperienced data-
wasted in this case is trivial, this becomes an
base designers (or those who have more experience important issue for very large databases.
with spreadsheets than databases) is to ignore the
2. Difficulty in making changes — What happens if
recommendation to model the domain of interest in the name of COMM 290 is changed to “Mathe-
terms of entities and relationships and to put all the
matical Optimization”? This would require the
information they need into a single, large table. same change to be made eight times. What if the
Figure 3.1 shows such a table containing information
person responsible for making the change for-
about courses and sections.
gets to change all the sections of COMM 290?
• If you have not already done so, open the What then is the “true” name of the course?
univ0_vx.mdb database.
3. Deletion problems — What if there is only one
• Open the Catalog View table. section of COMM 290 and it is not offered in a
The advantage of the single-table approach is that it particular year? If section 001 is deleted, then the
requires less thought during the initial stages of system no longer contains any information about
application development. The disadvantages are too the course itself, including its name and number
numerous to mention, but some of the most impor- of credits.
tant ones are listed below:


3. Relationships Introduction: The advantage of using tables and relation-

FIGURE 3.1: The “monolithic” approach to database design—the Catalog View table contains
information about courses and sections.

The course “COMM 290” consists
of many sections.

Each section has some information
unique to that section (such as
Time, Days, Building,
Room); however, the basic course
information (e.g., Title,
Credits) is the same for all
sections of a particular course.


3. Relationships Introduction: The advantage of using tables and relation-

4. Addition problems — If a new section is added to
FIGURE 3.2: A one-to-many relationship between
any course, all the course information has to be
Courses and Sections.
typed in again. Not only is this a waste of time, it
increases the probability of introducing errors into
the system.

3.1.1 “Normalized” table design
The problems identified above can be avoided by
spitting the Catalog View table into two separate
tables:
1. Courses— information about courses only
2. Sections — information about sections only. Access uses relationships in the following way:
The key to making this work is to specify a relation- Assume you are looking at Section 004 of
ship between Courses and Sections so that when COMM 290. Since Dept and CrsNum are included in
we look at a section, we know which course it the Sections table, and since a relationship line
belongs to (see Figure 3.2). Since each course can exists between the same two fields in the Courses
have one or more sections, such a relationship is table, Access can trace back along this line to the
called “one-to-many”. Courses table and find all the course-specific infor-
mation. All other sections of COMM 290 point back


3. Relationships Learning objectives

to the same record in the Courses table so the • Select Tools Relationships from the main
course information only needs to be stored once. menu.

Why do I want to represent my information in
In version 2.0 the menu structure is slightly
different. As such, you select Edit Relation-
ships instead.
multiple tables connected by relationships?
How do I create relationships in Access? • To add a table to the relationship window, select

How do I edit or change relationships?
Relationships Show Table from menu or press
the show table icon ( ) on the tool bar.
What is referential integrity and why is it • Perform the steps shown in Figure 3.3 to add the
important? Courses and Sections tables.
• Specify the relationship between the primary
3.3 Tutorial exercises key in Courses and the foreign key in Sec-
tions. This is shown in Figure 3.4.
3.3.1 Creating relationships between
tables Do not check cascading deletions or updates
• Close the Catalog View table and return to unless you are absolutely sure what they
mean. See on-line help if you are curious.
the database window.


3. Relationships Tutorial exercises

FIGURE 3.3: Add the Courses and Sections tables to the relationship window.

The rectangular “field list” represents a
table. Note that the key (or keys) composing double-click or presswish toRepeat aseither
Select the table you
Add.
add and
necessary.
the primary key are shown in bold type.

If you accidently add a table more than once, it
will show up with a table name_1 label.
To delete the extra version, click anywhere on
the unwanted rectangle and press the delete key.


3. Relationships Tutorial exercises

FIGURE 3.4: Create a relationship between the two tables.

on the “one” side ofkey
Select the primary
the foreign key on thefields onsidethe the
Drag the selected
“many”
to
of
relationship. relationship.

To select a concatenated
key (more than one If done
field) hold down the correctly, the
Control key while connectivity (1
selecting. to ∞) shows on
the relationship
line(s).
Ensure that the correct
fields are associated
with each other (this
must be done manually
for concatenated keys).

enforcethe box to
Check
referential
integrity.


3. Relationships Discussion

3.3.2 Editing and deleting relationships Note that simply deleting the table in the rela-
There are two common reasons for having to edit or tionship window does not delete the relation-
delete a relationship: ship, it merely hides it from view.

1. You want to change the data type of one of the
3.4 Discussion
fields in the relationship — Access will not let you
do this without first deleting the relationship (after
3.4.1 One-to-many relationships
you change the data type, you must re-create the
relationship). There are three types of relationships that occur in
2. You forget to specify referential integrity — if the data modeling:
“1” and “∞” symbols do not appear on the rela- 1. one-to-one — A one-to-one relationship exists
tionship line, then you have not checked the box between a student and a student number.
to enforce referential integrity. 2. one-to-many — A one-to-many relationship
In this section, assume that we have forgotten to exists between courses and sections: each
enforce referential integrity between Courses and course may consist of many sections, but each
Sections. section is associated with exactly one course.
• Perform the steps shown in Figure 3.5 to edit the 3. many-to-many — A many-to-many relationship
relationship between Courses and Sections. exists between students and courses: each stu-
dent can take many courses and each course
can contain many students.



FIGURE 3.5: Edit an existing relationship.

The missing “1” and “∞” symbols
indicate that referential integrity has
not been enforced.
the joiningrelationshipon either lineon
Select the
line (click
by clicking
if
the key is concatenated). If you do
this correctly, the line becomes
darker.

click to get the edit/delete pop-up
With the relationship selected, right-
menu. If you do not get this menu,
make sure you have correctly
selected the relationship.



Although the data modeling technique used most “many” side of a relationship has a corresponding
often in information system development—Entity- record on the “one” side.
Relationship diagraming—permits the specifica- Enforcing referential integrity means that you cannot,
tion of many-to-many relationships, these relation- for instance, create a new record in the Sections
ships cannot be implemented in a relational table without having a valid record in the Courses
database. As a consequence, many-to-many rela- table. This is because having a section called
tionships are usually broken down into a series of “BSKW 101 Section 001” is meaningless unless
one-to-many relationships via “composite entities” there is a course called “BSKW 101”. In addition, ref-
(alternatively, “bridging tables”). Thus to implement erential integrity prevents you from deleting records
the student-takes-course relationship, three tables on the “one” side if related records exist on the
are used: Students, Courses, and Student- “many” side. This eliminates the problem of
TakesCourse. “orphaned” records created when parent records are
deleted.
3.4.2 Referential integrity
Referential integrity is especially important in the
One important feature of Access is that it allows you context of transaction processing systems. Imagine
to enforce referential integrity at the relationship that someone comes into your store, makes a large
level. What is referential integrity? Essentially, refer- purchase, asks you to bill customer number “123”,
ential integrity means that every record on the and leaves. What if your order entry system allows
you to create an order for customer “123” without


3. Relationships Application to the assignment

first checking that such a customer exists? If you A primary key and a foreign key must be of
have no customer 123 record, where do you send the same data type before a relationship can
the bill? be created between them. Because of this, it
In systems that do not automatically enforce referen- is important to remember that the autonumber
tial integrity, these checks have to be written in a pro- data type (or counter in version 2.0) is really a
gramming language. This is just one example of how long integer.
table-level features can save you enormous pro-
It never makes sense to have a relationship
gramming effort.
between two autonumber fields. A foreign key
Enforcing referential integrity has obvious cannot be an autonumber since referential
implications for data entry: You cannot popu- integrity constraints require it to take on a an
late the “many” side of the table until you pop- existing value from a parent table.
ulate the “one” side.

3.5 Application to the assignment
• Specify all relationships—including referential
integrity constraints—between tables in your sys-
tem. You are not responsible for cascading
updates/deletions in this assignment.


Access Tutorial 4: Basic Queries Using QBE
4.1 Introduction: Using queries to Once a query is defined, it can be used in exactly the
get the information you need same way as a table. Because of this, it is useful to
think of queries as “virtual tables”. Similarly, in some
At first glance, it appears that splitting information
DBMSes, queries are called “views” because they
into multiple tables and relationships creates more of allow different users and different applications to
a headache than it is worth. Many people like to
have different views of the same data.
have all the information they need on one screen
(like a spreadsheet, for instance); they do not want to
have to know about foreign keys and relationships
and so on. Do queries contain any data?

Queries address this problem. They allow the user to How do I create a query?
join data from one or more tables, order the data in What can I do with a query?
different ways, calculate new fields, and specify cri-
teria to filter out certain records.
How do I create a calculated field?

The important thing is that the query itself contains
Why does Access add square brackets
around field names?
no data—it merely reorganizes the data from the
table (or tables) on which it is built without changing What names should I give the queries I
the “underlying tables” in any way. create?
What does the ampersand operator () do?


4. Basic Queries Using QBE Tutorial exercises

What is a non-updatable recordset? How do I 4.3.2 Five basic query operations
tell whether a query results in a non-
4.3.2.1 Projection
updatable recordset?
Projecting a field into a query simply means includ-
4.3 Tutorial exercises ing it in the query definition. The ability to base a
query on a subset of the fields in an underlying table
4.3.1 Creating a query (or tables) is particularly useful when dealing with
tables that contain some information that is confiden-
• Use the New button in the Queries pane of the
tial and some that is not confidential. For instance,
database window to create a new query as
the Employees table you created in Tutorial 2 con-
shown in Figure 4.1.
tains a field called Salary. However, most of the
• Add the Courses table to the query as shown in
queries seen by end-users would not include this
Figure 4.2.
information, thereby keeping it private.
• Examine the basic elements of the query design
• Perform the steps shown in Figure 4.4 to project
screen as shown in Figure 4.3.
the DeptCode, CrsNum, and Title fields into
• Save your query (Control-S) using the name
the query definition.
qryCourses.
• Select View Datasheet from the menu to see
the results of the query. Alternatively, press the
datasheet icon ( ) on the tool bar.



FIGURE 4.1: Create a new query.

the database window. in
Select the Queries tab

createthenew query. to
Press
a
New button

Avoid the use of the query wizard
at this point. Queries are very
important and it is best to learn to
create them from scratch.



FIGURE 4.2: Add tables to your query using the “show table” window.

by selecting it and pressing Addquery
Add the Courses table to the
(alternatively, you can simply double-
click on the table you want to add).

table”Close when“modal”—you can
Press
window is
done (the “show The “show table” window is always
available from the Query Show Table
not do anything else in Access until a menu. Alternatively, you can press the
modal window is closed). “show table” button on the tool bar.



FIGURE 4.3: The basic elements of the query design screen.

The upper If you “lose” tables in the top
pane contains pane, you have to use the
field lists for horizontal and vertical scroll
the tables on bars to return to the upper-left
which the corner of the pane.
query is based.
Field row— shows the name of the
fields included in the query.

The lower Table row— shows the name of the
pane contains table that the field comes from. To get
the actual table names in version 2.0, select View
query Table Names from the menu.
definition.
Sort row— allows you to specify the
order in which the records are
Criteria row — allows you Show boxes— determine displayed
to specify criteria for whether fields included
including or excluding in the query are actually
records from the results set. displayed.



FIGURE 4.4: Project a subset of the available fields into the query definition.

drag it the field querywish to project and
Select
into the
you
definition grid.
Alternatively, double-click the field.

To project all the fields in the
Courses table (including
any that might be added to the
table after this query is
created) drag the asterisk (*)
into the query definition grid.

To save time when
projecting fields, select more
than one field at once (by
holding down the Control
key) and dragging all the
fields as a group.



• Select View Query Design to return to design 4.3.2.3 Selection
mode. Alternatively, press the design icon ( ) You select records by specifying conditions that each
on the tool bar. record must satisfy in order to be included in the
4.3.2.2 Sorting results set. In “query-by-example” you enter exam-
ples of the results you desire into the criteria row.
When you use a query to sort, you do not change the
physical order of the records in the underlying table • Perform the steps shown in Figure 4.6 to select
only those courses with a DeptCode = “COMM”.
(that is, you do not sort the table). As a result, differ-
ent queries based on the same table can display the 4.3.2.4 Complex selection criteria
records in different orders. It is also possible to create complex selection criteria
• Perform the steps shown in Figure 4.5 to sort the using Boolean constructs such as AND, OR, and
results of qryCourses by DeptCode and NOT.
CrsNum. • Project the Credits field into the query.
• Perform the steps shown in Figure 4.7 to create a
Since a query is never used to display data to
query giving the following result:
a user, you can move the fields around within
“Show the department, course number, and title
the query definition to get the desired sorting
of all courses in the Commerce department for
precedence. You then reorder the fields in the
which the number of credits is greater than
form or report for presentation to the user.
three.”



FIGURE 4.5: Sorting the results set on one or more fields.

and “descending” for the CrsNum field.field
Select “ascending” for the DeptCode

When multiple sort fields are specified,
the sorting precedence is from left to
right (e.g., DeptCode is sorted first
the order of the records.
View the results and notice and then CrsNum is sorted within each
set of matching DeptCodes).



FIGURE 4.6: Select a subset of records from the Courses table matching a specific criterion.

of the the expression “COMM”could also typerow
Type
DeptCode field. You
in the criteria

= “COMM” but the equal sign is always implied
unless another relational operator is used.

matching results. Only records
View the
the criteria are shown.



FIGURE 4.7: Select records using an AND condition.

When multiple criteria are placed in the
same row, they are AND-ed. In other
words, the records in the results set
Show the result. must satisfy DeptCode = “COMM”
AND Credits 3.

Note that the number
3 is not in quotation
marks whereas the
string of characters
“COMM” is.

Uncheck the “show”
box (Credits is
used as a criterion but
“COMM” first criteria:
Enter the
the same row, enter the second
In
3
it is not displayed in
the results set)



• Perform the steps shown in Figure 4.8 to create a • Project Title from the Courses table and
query giving the following result: DeptCode, CrsNum, Section and Catalog-
“Show the department, course number, and title Num from the Sections table (see Figure 4.9).
of all courses from the Commerce department • Follow the instructions in Figure 4.10 to move
and also show those from the Creative Writing CatalogNum to the far left of the query definition
department for which the number of credits is grid.
greater than three.” Access performs an automatic lookup of information
4.3.2.5 Joining from the “one” side of the relationship whenever the
a valid value is entered into the foreign key of the
In Tutorial 3, you were advised to break you informa-
“many” side of the relationship. To see how this
tion down into multiple tables with relationships
between them. In order to put this information back works, create a new section of “MUSC 105”:
• Scroll to the bottom of the query in datasheet
together in a usable form, you use a join query.
• Close qryCourses. mode and click on the department field.
• Open the relationships window and ensure you • Enter “MUSC”.
have a relationship defined between Courses • Enter “105” in the course number field.
and Sections. If you do not, create one now (do Once Access knows the DeptCode and CrsNum of
not forget to enforce referential integrity). a section, it can uniquely identify the course that the
• Create a new query called qryCatalogNum section belongs to (which means it also knows the
based on the Courses and Sections tables. values of Title, Credits, Activity, etc.)



FIGURE 4.8: Select records using an AND and an OR condition.

When multiple criteria are placed in
different rows, then they are OR-ed. In
other words, the records in the results set
must satisfy DeptCode = “COMM”
OR (DeptCode = “CRWR” AND
Credits 3).

criterion in the
Enter the Credits

DeptCode
Enter the second row.
criteria in
different rows.



FIGURE 4.9: Create a query that joins Courses and Sections.

Note that the relationship betweeninto the query.
Bring Courses and Sections
the tables is
inherited from the relationship window.

the query definition.both tables into
Project fields from



FIGURE 4.10: Move a field within the query definition grid.

“column selector”grey
Click once on the
above the field you
want to move (if
properly selected, the
column turns black).

To delete a field from
the query definition,
select it and press the
Delete key.

its new location. column to
Drag the selected



4.3.3 Creating calculated fields the expression involves two fields from the Courses
A calculated field is a “virtual field” in a query for table (DeptCode and CrsNum) and the ampersand
which the value is a function of one or more fields in operator (see Section 4.4.2 for more information on
the underlying table. To illustrate this, we will create using the ampersand operator).
two calculated fields: • Create a new query called qryCourseLengths
based on the Courses table.
1. one to combine DeptCode and CrsNum into one
• Follow the instructions in Figure 4.11 to create
field,
the calculated field Course
2. one to translate the Credits field into a dichoto-
• Run the query to verify the results, as shown in
mous string variable (full year or half
Figure 4.12.
year).
The syntax of a calculated field is always the same: When you use field names in expressions,
calc field name: definition Access normally adds square brackets. This
For example, the syntax for the calculated field is not cause for concern because in Access,
called Course is: square brackets simply indicate the name of a
Course: DeptCode CrsNum field (or some other object in the Access envi-
ronment). However, if your field name con-
The calculated field name can be just about any-
tains blank spaces (e.g., Dept Code), the
thing, as long as it is unique. The definition is any
square brackets are NOT optional—you must
expression that Access can evaluate. In this case,



FIGURE 4.11: Create a calculated field based on two other fields.

The zoom window provides more room to type than the tiny
space in the query definition grid. Invoke the zoom window
by moving to the area of the grid in which you wish to type
and either right-click or press the Shift-F2 keys.

the Field row of
Put the cursor in

the first column
and invoke the
zoom window.

and the definition
Type in the name
Press OK when you
of the calculated have finished typing
field. The name the expression.
cannot be the same
as that of an
existing field.



FIGURE 4.12: The resulting calculated field.

The name of the
calculated field shows in
the field selector.

When the zoom window is
closed, Access adds square
brackets to the field names.
Since the field names in this
example do not contain
spaces, the brackets are
optional.

The ampersand operator () simply tacks
CrsNum onto the end of DeptCode.



type them every time you use the field name three credits is a full-year course). To do this, we will
in an expression. use the “immediate if” (iif) function.
• Search on-line help for information about the
4.3.3.1 Refining the calculated field iif() function.
Instead of having DeptCode and CrsNum run Basically, the function uses the following syntax:
together in the new Course field, you may prefer to
iif(expression, true part,
have a space separating the two parts. false part)
• Edit the Courses field by clicking on the field row
to implement the following logic:
and invoking the zoom box.
IF expression = TRUE THEN
• Add a space (in quotation marks) between the
RETURN true part
two constituent fields:
ELSE
Course: DeptCode ” ” CrsNum
RETURN false part
• Switch to datasheet mode to see the result.
END IF
4.3.3.2 A more complex calculated field • Create a new calculated field called Length:
To create a calculated field that maps Credits to a Length: iif(Credits 3, “full
dichotomous string variable, we need a means of year”, “half year”)
testing whether the value of Credits exceeds a • Verify the results, as shown in Figure 4.13.
certain threshold (e.g., any course with more than



FIGURE 4.13: Create a calculated field using the “immediate if” function

Length: iif(Credits3, “fullwith the following expression:
Create a calculated field called Length
year”, “half year”)


4. Basic Queries Using QBE Discussion

4.3.4 Errors in queries 4.4 Discussion
It may be that after defining a calculated field, you
get the “enter parameter” dialog box shown in 4.4.1 Naming conventions for database
Figure 4.14 when you run the query. This occurs objects
when you spell a field name incorrectly. Access can- There are relatively few naming restrictions for data-
not resolve the name of the misspelled field and thus base objects in Access. However, a clear, consistent
asks the user for the value. To eliminate the problem, method for choosing names can save time and avoid
simply correct the spelling mistake. confusion later on. Although there is no hard and fast
FIGURE 4.14: A spelling error in a calculated naming convention required for the assignment, the
field. following points should be kept in mind:
• Use meaningful names — An object named
Table1 does not tell you much about the con-
Access cannot find the tents of the table. Furthermore, since there is no
field named Creditz practical limit to the length of the names, you
should not use short, cryptic names such as
s96w_b. As the number of objects in your data-
base grows, the time spent carefully naming your
objects will pay itself back many times.



• Use capitalization rather than spaces to separate • Stick to standard alphanumeric characters — You
words — Unlike many database systems, Access should limit yourself to the characters [A...Z],
allows spaces in object names. However, if you [a...z], [0...9], and perhaps underscore (_) and
choose to use spaces, you will have to enclose dash (-). Although Access allows you to use virtu-
your field names in square brackets whenever ally any character, undocumented problems have
you use them in expressions (e.g., [Back been encountered in the past with non-alphanu-
Orders]). As such, it is slightly more efficient to meric characters such as the pound sign (#).
use a name such as BackOrders than Back Table 4.1 shows a suggested naming convention for
Orders. Access database objects (you will discover what
• Give each type of object a distinctive prefix (or these objects are in the course of doing the tutorials).
suffix) — This is especially important in the con-
text of queries since tables and queries cannot 4.4.2 The ampersand () operator
have the same name. For example, you cannot
The ampersand operator is like any other operator
(e.g., +, -, ×, ÷) except that it is intended for use on
have a table named BackOrders and a query
named BackOrders. However, if all your query
strings of characters. What the ampersand does is
names are of the form qryBackOrders, then
simply add one string on to the end of another string
distinguishing between tables and queries is
(hence its other name: the “concatenation” operator).
straightforward.
For example, the expression
“First string” “Second string”



Table 4.1: A suggested naming convention for yields the result
Access database objects. First stringSecond string
However, if a space is include within the quotation
Object type Prefix Example marks of the second string (“ Second string”),
table (none) OrderDetails the result is:
query qry qryNonZeroBackOrders First string Second string
parameter pqry pqryItemsInOrder
query 4.4.3 Using queries to populate tables
form frm frmOrders on the “many” side of a
relationship
sub form sfrm sfrmOrderDetails
In Section 4.3.2.5, you added a record to the Sec-
switchboard swb swbMainSwitchboard
form tions table to demonstrate the automatic lookup
feature of Access. However, a common mistake
report rpt rptInvoice
when creating queries for entering data into tables
sub report srpt srptInvoiceDetails on the “many” side of a relationship is to forget to
macro mcr mcrOrders project the table’s foreign key. That is, faced with two
Visual Basic bas basUtilities tables containing the fields DeptCode and CrsNum,
module you project the fields from the wrong table (the “one”
side) into your query definition.



To illustrate the problem, do the following: 4.4.4 Non-updatable recordsets
• Open the qryCatalogNum query and make the Another problem that sometimes occurs when creat-
changes shown in Figure 4.15. ing join queries is that the query is not quite right in
• Attempt to save the new section of “MUSC 105” some way. In such cases, Access will allow you to
as shown in Figure 4.16. view the results of the query, but it will not allow you
There are two ways to avoid this error when deciding to edit the data.
which fields to project into your join queries: In this section, will look at a nonsensical query that
1. Always show the table names when creating a results from an incompletely specified relationship.
query based on more than one table. That way, As you will probably discover, however, there are
you can quickly determine whether the query many different way to generate nonsensical queries.
makes sense. • Create a new query called qryNonUpdate
2. Always ask yourself: “What is the purpose of this based on the Courses and Sections tables.
query?” If the answer is: “To add new records to • Delete the CrsNum relationship but leave the
the Sections table,” you automatically have to DeptCode relationship intact, as shown in
include all the fields from the Sections table. Figure 4.17.
Fields from the Courses table are only shown The result of this query is that every section in a
for validation purposes. Commerce course will be associated with every
Commerce course. Since allowing the user to update



FIGURE 4.15: Create a data-entry query without a foreign key.

In version 2.0 you have to
Reorder the fields (by
dragging and dropping) so
select View Table
Names to display the
that DeptCode and table row.
CrsNum are on the far left.

DeptCodesource table for
Change the
and CrsNum
from Sections to
Courses.

Switch to datasheet mode
and attempt to add a new
section of “MUSC 105”.



FIGURE 4.16: The result of attempting to save a record in which the foreign key is missing

Since the fields are bound to the
Courses table, you are
attempting to replace the
current record in the Courses
table with “MUSC 105”. But
since a “MUSC 105” already
exists, you get an error.

new sectionsave the
Attempt to
by
clicking its record
selector.



FIGURE 4.17: Create a non-updatable recordset.

view thefields fromdatasheet mode
Project
query in
both tables and
(i.e., view the “recordset”).

Attempt to
change a value in
the recordset.

CrsNum relationship byquery, deleteitthe
To create a nonsensical
clicking on Note the absence of the asterisk and the “new record”
and pressing the Delete key. Leave the row. This is a sure sign that the recordset is non-updatable.
DeptCode relationship intact.


4. Basic Queries Using QBE Application to the assignment

the values in this recordset would create anomalies, should appear automatically. If they do not, see
Access designates the recordset as non-updatable. Section 4.4.3.
• Create a calculated field in your qryOrderDe-
A common mistake is to build data entry tails query that calculates the extended price
forms on nonsensical queries and to assume (quantity shipped × price) of each order detail.
that there is a mistake in the form when the • Enter the first order into your system by entering
forms do not work. Clearly, if a query is non- the information directly into tables or queries.
updatable, a form based on the query is also This involves creating a single Orders record
going to be non-updatable. A quick check for and several OrderDetails records. You must
a “new record” row in the query can save time also consult the Products and BackOrders
and frustration. tables to determine the quantity of each item to
ship.
• Create a query to sort the Products table by Entering orders into your system will be much
ProductID. less work once the input forms and triggers
• Create a query that joins the OrderDetails are in place. The goal at this point is to get
and Products tables. When you enter a valid you thinking about the order entry process
ProductID, the information about the product and ways in which it can be automated.
(such as name, quantity on hand, and so on)


Access Tutorial 5: Basic Queries using SQL
5.1 Introduction: The difference Although you normally use QBE in Access, the ubiq-
between QBE and SQL uity of SQL in organizations necessitates a brief
overview.
Query-By-Example (QBE) and Structured Query
Language (SQL) are both well-known, industry-stan-
dard languages for extracting information from rela-
tional database systems. The advantage of QBE (as What is the difference between QBE and
you saw in Tutorial 4) that it is graphical and rela- SQL?
tively easy to use. The advantage of SQL is that it How do I create an SQL query?
has achieved nearly universal adoption within the
relational database world. 5.3 Tutorial exercises
With only a few exceptions (which you probably will In this section, you will create a few simple queries in
not encounter in this assignment) QBE and SQL are SQL.
completely interchangeable. If you understand the • Create a new query but close the “show table”
underlying concepts (projection, selection, sorting, dialog box with out adding tables.
joining, and calculated fields) of one, you understand • Select View SQL to switch to the SQL editor as
the underlying concepts of both. In fact, in Access shown in Figure 5.1.
you can switch between QBE and SQL versions of
your queries with the click of a mouse.

Last update: 22-Aug-1997 Home Previous 1 of 5 Next

5. Basic Queries using SQL Tutorial exercises

2. … FROM table … — specifies the underlying
FIGURE 5.1: Open a query in SQL mode table (or tables) for the query;
3. … WHERE condition1 AND/OR
condition2, …, AND/OR conditionn —
specifies one or more conditions that each record
must satisfy in order to be included in the results
set;
4. ; (semicolon) — all SQL statements must end
with a semicolon (but if you forget it, Access will
add it for you).
5.3.1 Basic SQL queries These can now be put together to build an SQL
A typical SQL statement resembles the following: query:
SELECT DeptCode, CrsNum, Title FROM • Type the following into the SQL window:
Courses WHERE DeptCode = “COMM”; SELECT DeptCode, CrsNum, Title FROM
There are four parts to this statement: Courses WHERE DeptCode = “COMM”;
• Select View Datasheet to view the results.
1. SELECT field1, field2, …, fieldn …
— specifies which fields to project (the DIS- • Select View Query Design to view the query in
QBE mode, as shown in Figure 5.2.
TINCTROW predicate shown in Figure 5.1 is
optional and will not be discussed in this tutorial); • Save your query as qryCoursesSQL.



FIGURE 5.2: The SQL and QBE views are interchangeable.

When you return to SQL mode
after viewing your query in QBE
mode, you will notice that Access
has added some additional text.
This optional text does not
change the query in any way



5.3.2 Complex WHERE clauses 5.3.3 Join queries
You can use AND, OR, and NOT conditions in your Join queries use the same elements as a basic
WHERE clauses in a straightforward manner. select query. The only difference is that the FROM
• Change your query to the following to get all statement is replaced with a statement that
Commerce courses with more than three credits: describes the tables to be joined and the relationship
SELECT DeptCode, CrsNum, Title (i.e., foreign key) between them:
FROM Courses ... FROM table1 INNER JOIN table2 ON
WHERE DeptCode = “COMM” AND Credits table1.field1 = table2.field2 ...
3 Note that since both tables contain the fields Dept-
Code and CrsNum, the table name.field
Note that since DeptCode is a text field, its
name notation must be used to remove any ambi-
criterion must be a string (in this case, the lit-
guity.
eral string “COMM”). However, Credits is a
• Create a new SQL query containing the text:
numeric field and its criterion must be a num-
SELECT Courses.DeptCode,
ber (thus, there cannot be quotation marks
Courses.CrsNum, Courses.Title,
around the 3).
Sections.CatalogNum
FROM Courses INNER JOIN Sections ON
Courses.CrsNum = Sections.CrsNum


5. Basic Queries using SQL Discussion

AND Courses.DeptCode =
Sections.DeptCode
WHERE Courses.DeptCode=”COMM”;

5.4 Discussion
Although the syntax of SQL is not particularly diffi-
cult, writing long SQL queries is tedious and error-
prone. For this reason, you are advised to use QBE
for the assignment.
In the real world, however, when you say you know
something about databases, it usually implies you
know the “data definition” and “data manipulation”
aspects of SQL in your sleep. If you plan to pursue a
career in information systems, a comprehensive
SQL reference book can be a worthwhile investment.


Access Tutorial 6: Form Fundamentals
6.1 Introduction: Using forms as FIGURE 6.1: The relationship between forms,
the core of an application queries, and tables.
Forms provide a user-oriented interface to the data
in a database application. They allow you, as a forms
developer, to specify in detail the appearance and
behavior of the data on screen and to exert a certain
amount of control over the user’s additions and mod- queries
ifications to the data.
Like queries, forms do not contain any data. Instead,
they provide a “window” through which tables and tables
queries can be viewed. The relationship between Courses Departments Employees
tables, queries, and forms is shown in Figure 6.1.
In this tutorial, we are going to explore the basic ele-
ments of form creation using Access’ form design 6.2 Learning objectives
tools. In subsequent tutorials, we will extend the Do forms contain data?
functionality and ease-of-use of our basic forms with
subforms (Tutorial 7), “combo box” controls
How do I create a form?

(Tutorial 8), and triggers (Tutorial 13).


6. Form Fundamentals Tutorial exercises

How do I make the contents of a field on a • Create a new blank form based on the Courses
form read-only? table, as shown in Figure 6.2.
What is an unbound text box? How do I create • The basic elements of the design screen are
one? shown in Figure 6.3. Use the View menu to dis-

How do I create a form using the form wizard?
play the toolbox and field list if they are not
already visible.
What is the difference between a columnar
6.3.1.1 Adding bound text boxes
(single-column) and tabular form?
• Add a “bound” text box for the DeptCode field by
dragging DeptCode from the field list to the form
6.3 Tutorial exercises background, as shown in Figure 6.4.
• Reposition the DeptCode text box in the upper
6.3.1 Creating a form from scratch left of the form.
Although Access provides an excellent wizard for
creating simple forms, you will start by building a Remember that you can always use the
form from scratch. This will give you a better appreci- “undo” feature to reverse mistakes. Select
ation of what it is the wizard does and provide you Edit Undo from the menu or simply press
with the basic knowledge needed to customize and Control-Z (this works the same in virtually all
refine the wizard’s output. Windows applications).



FIGURE 6.2: Create a new form to display data from the Courses table.

the database window. from
Select the Forms tab

use theDesign at this (do not
Select
wizard
View
point)
Bind the form to the
Courses table.

Since you can build a form on top of a table or a
query, both are shown in this list (here is where a
meaningful naming convention starts to pay off)



FIGURE 6.3: The basic elements of the form design screen.

To change the size of
the form, drag the edges
of the detail section.

The field list — shows the fields The toolbox — the icons in the If the field list and toolbox
in the table or query to which the toolbox are used to create graphical are not displayed, use the
form is bound. items and controls on the form. View menu or toolbar icons.



FIGURE 6.4: Create a bound text box for the DeptCode field.

Access uses the field’s caption property as the default label for the text box.
If no caption is specified, the field name (e.g., DeptCode) is used. To save
time editing labels, choose your captions with this feature in mind.

to thethe highlightedsection.on
Drag
form’s detail
field

To move an object and its
label, drag the center of the
object (the cursor becomes
a white arrow). To move
just the object or just the
label, drag the upper left
handle (the cursor becomes
a pointing finger).
field inthe DeptCode
Select
the field list.



• Drag the remaining fields on to the form, as • Scroll down the property sheet to the Locked
shown in Figure 6.5 (do not worry about whether property and set it to Yes, as shown in
the fields are lined up perfectly). Figure 6.7.
• Select View Form to see the resulting form. • Switch to the form view and attempt to change
Alternatively, press the form view icon ( ). the contents of the DeptCode field.
• Select View Form Design or press the design A stronger form of protection than locking a field is
view icon ( ) to return to design mode. “disabling” it.
6.3.1.2 Using a field’s properties to protect its • Return to design mode and make the following
contents changes: reset the Locked property to No; set the
Every object on an Access form (e.g., text box, label, Enabled property to No.
• Attempt to change the contents of the DeptCode
detail section, etc.) has a set of properties that can
be modified. In this section, you are going to use the field in form view, as shown in Figure 6.8.
• Save the form as frmCourses.
Locked and Enabled properties to control the user’s
ability to change the information in a field. 6.3.1.3 Adding an unbound text box
• Select the DeptCode text box and right-click to All the text boxes created in the previous section
bring up its property sheet, as shown in were “bound” text boxes—that is, they were bound to
Figure 6.6. a field in the underlying table or query. When you
change the value in a bound text box, you are mak-



FIGURE 6.5: Add the text boxes and switch to form view to see the resulting form.

Text boxes are simply
“windows” on to the fields
in the underlying table.

fieldsthe the form.
Add
to
remaining main menu toview the form.
Select View Form from the

You can add more than one field to the form with one
drag-and-drop operation by holding down the Control
button when selecting the fields from the field list.



FIGURE 6.6: Bring up the property sheet for the DeptCode text box.

object to getoncepop-up selected
Right-click
the
on the
menu.

Select Properties to get the
property sheet.

DeptCode text box) for
Select the object (e.g., the The properties are broken down
into four groups. To see all the
which you wish to see the properties, select the All tab.
properties. When an object
has been selected, it is
bordered by six dark
“handles”. Some properties of the text box (such as
input mask) are inherited from the field
to which the text box is bound.



ing the change directly to the data in the underlying
FIGURE 6.7: Change the Locked property of
table.
DeptCode to Yes.
It is possible, however, to create objects on forms
that are not bound to anything. Although you will not
use many “unbound” text boxes in the assignment, it
is instructive to see how they work.
• Create a new empty form bound to the Courses
table and save it using the name
frmCoursesUB.
• Select the text box tool ( ) from the toolbox and
create and unbound text box, as shown in
Figure 6.9.
6.3.1.4 Binding an unbound text box to a field
The only difference between a bound and an
unbound text box is that the Control Source property
of a bound text box is set to the name of a field. In
this section, you are going to change the unbound
the Locked property.find
Use the scroll bar to
text box shown in Figure 6.9 to a bound text box.



FIGURE 6.8: Set the Enabled property of DeptCode to No and attempt to change the value in the
field.

Enabled to No. and
Set Locked to No

to see the result.view
Switch to form

When a form object is disabled, it
cannot receive the “focus” (that is,
you cannot put the cursor on it).

By default, disabled form objects are
greyed out. To override this feature,
set the Locked property to Yes and
the Enabled property to No.



• Bring up the property sheet for the unbound text
FIGURE 6.9: Create an unbound text box.
box. Change its Control Source property from null
to DeptCode, as shown in Figure 6.10.
The cursortext box toolsmall texttoolbox.
Select the
becomes a
from the
box.
6.3.2 Creating a single-column form
using the wizard
Now that you understand the basics of creating and
modifying bound text boxes, you can rely on the form
wizard to create the basic layout of all your forms.
• Create a new form bound to the Courses table
using the form wizard, as shown in Figure 6.11.
• Use the form wizard to specify the fields you want
on your form and the order in which they appear,
detail section to create a
Click anywhere on the
as shown in Figure 6.12. Select “columnar” when
new unbound text box. prompted for the form type.

“Columnar” forms are called “single column”
forms in version 2.0.



FIGURE 6.10: Set the Control Source property FIGURE 6.11: Create a new form using the form
of an unbound text box. wizard.

wizard.the form
Select

Courses table. the
Bind the form to

the Control Source property
Use the pull-down list to set

to DeptCode.



FIGURE 6.12: Use the form wizard to determine the order of fields on your form.

The order in which
the fields appear in
this pane is the order
in which they will
appear on the form.
Use the and
buttons to move
fields back to the
pane on the left.
to show a field, either double-
click it or press the button.

To show all the fields, press the
button.


6. Form Fundamentals Discussion

The primary advantage of the wizard is that it auto- look and behavior of the data. The three different
matically creates, formats, and aligns the bound text types of forms are shown in Figure 6.13.
boxes. Of course, once the wizard has created a
form, you are free to modify it in any way. 6.5 Application to the assignment
• Use the wizard to create columnar forms for all
If you make a mistake when creating a form your master tables. Note that in some cases
(e.g., you put the fields in the wrong order) it (e.g., BackOrders) you will want to base the
is often easier to use the wizard and start over form on a join query rather than table in order to
than to fix the problem manually. show important information such as CustName
and ProductName.
6.4 Discussion
6.4.1 Columnar versus tabular versus
datasheet forms
Columnar forms show one record per page. Tabular
forms, in contrast, show many records per page and
are used primarily as subforms. There is also a a
datasheet form type, but it is seldom used since it
gives the developer relatively little control over the


6. Form Fundamentals Application to the assignment

FIGURE 6.13: The same information displayed as a columnar, tabular, and datasheet form.

A columnar form displays
one record per page.

A tabular form
displays more than
one record per page.

A datasheet form is identical to the datasheet
view of a table or query. Since it gives the
designer very little control over the format of the
data, it is generally inappropriate for use in an
end-user application.


Access Tutorial 7: Subforms
7.1 Introduction: The advantages of fact, there is no need to show DeptCode and
forms within forms CrsNum in the subform).
Although you will quickly learn to take a feature such
A columnar/single-column main form with a tabular
as form/subform synchronization for granted, it is
subform is a natural way of representing information
from tables with a one-to-many relationship. For worthwhile to consider what this feature does and
what it would take if you had to implement the same
example, the form shown in Figure 7.1 is really two
forms: the main form contains information about a feature using a programming language.
specific course; the subform shows all the sections
associated with the course. 7.2 Learning objectives
In the Courses and Sections example, the foreign What is form/subform synchronization?
key (DeptCode and CrsNum) provides a link How do I create a form/subform combination?
between the two forms. This connection allows
Access to synchronize the forms, meaning:
How do I link a form with a subform?

• when you move to another course record, only
7.3 Tutorial exercises
the relevant sections are shown in the subform;
• when you add a new section, the foreign key in Although there are a number of different ways to cre-
the Sections table is automatically filled in (in ate a subform within a main form, the recommended
procedure is the following:


7. Subforms Tutorial exercises

FIGURE 7.1: A typical form/subform combination.

Because a link is established between the main form
and the subform, only the sections that belong with
“COMM 351” are displayed in the subform.

The main part of the form is
columnar (one record per page)
and displays information from
the Courses table.

The subform is a separate
tabular form that displays
information from the
Sections table.



1. create and save both forms (one columnar, one space they occupy. A number of editing issues
tabular) separately; are highlighted in Figure 7.5.
2. drag the subform on to the main form; and, • Save the form as sfrmSections and close it.
3. verify the linkage between the two forms.
7.3.3 Linking the main form and subform
7.3.1 Creating the main form In this section, you are going to return to the main
• Use the wizard to create a columnar form based form and drag the saved subform from the database
on the Courses table. window to an appropriate position on the main form.
• Rearrange the fields so that they make efficient • Open the main form (frmCoursesMain) in
use of the top part of the form, as shown in design mode.
Figure 7.2. • Select Window univ0_vx: Database to open the
• Save the form as frmCoursesMain. database window in the foreground. Alternatively,
you can press the database window icon ( ) on
7.3.2 Creating the subform the tool bar.
• Use the wizard to create the subform, as shown • Perform the steps shown in Figure 7.6 to drag the
in Figure 7.3 and Figure 7.4. subform on to the main form.
• Subforms created by the wizard typically require • The result of the drag-and-drop operation are
some fine tuning in order to reduce the amount of shown in Figure 7.7. The advantage of the drag-
and-drop method of creating a sub form is that



FIGURE 7.2: Rearrange the text boxes on the main form to make room for the subform.

columnar form based on a
Use the wizard to create
Courses.

rearrange the text boxes to
Enter form design mode and
make room for the subform.

Save the form under the name
frmCoursesMain.

To move more than one form object at a time, either
hold down the Shift key when selecting or drag a box
through the objects (click and drag to create a box).



FIGURE 7.3: Use the wizard to create the Sections subform (part 1).

DeptCodeneedCrsNum since they
There is no
and
to include

are shown in the main form.

The order in which the fields are added to
the right-hand pane determines their order
(from left to right) on the form. Use the
and buttons to get the desired ordering.

new form to thewizard and bind the
Select the form
Sections table.



FIGURE 7.4: Use the wizard to create the Sections subform (continued)

In version 7.0, the title appears in the bar
across the top of the form’s window. In
version 2.0, however, the wizard creates a
title in a form header. As such, you
should ensure this is blank if you are
using version 2.0.
Select Tabular
layout.

form, you do not is embedded in aamain
Since a subform
have to provide title.

Select Modify the form’s design to
enter form design mode directly.



FIGURE 7.5: Edit the subform to reduce the amount of space it uses.

“detail band” and bringingby moving footer” band to the
Reduce the vertical space
the “form
the fields up
up
by the headings and fields. used
Reduce the horizontal space against the fields (to move a band, drag it using the mouse).

To split the headings into two
or more lines, place the cursor
at the desired split location and
press Shift-Enter.

To move all the fields at once,
drag a “selection box” so that it
touches each field. Note that the
box does not have to enclose
objects for them to be selected.



FIGURE 7.6: Drag the subform on to the main form.

in design mode.form
Open the main

window so that the
Position the database

subform’s target
destination is visible.

Drag the subform on
to the main form.



the width of the subform control (the white win- Since both the forms created in Section 7.3.3 were
dow) is automatically set to equal the width of the built on tables, Access could automatically deter-
subform. mine the relationship.
• Verify the link between the form and the subform
If you make changes to the size of your sub- by examining the property sheet of the subform
form once the subform control is created, you control, as shown in Figure 7.8.
may have to resize the subform control by
clicking and dragging a corner handle. The terminology “link child field” and “link
master field” is identical to “foreign key” and
7.3.4 Linking forms and subforms “primary key”. The main form is the parent
manually (“one” side) and the subform is the child
If both the form and the subform are based on (“many” side).
tables, and if relationships have been defined
• View the resulting form. Notice that as you move
between the tables, Access normally has no problem
from course to course, the number of sections
determining which fields “link” the information on the
shown in the subform changes (see Figure 7.9).
main form with the information in the subform. How-
ever, when the forms are built on queries, Access
has no relationship information to rely on. As such,
you have to specify the form/subform links manually.



FIGURE 7.7: The drag-and-drop operation creates a subform control.

The white area is a
“subform control”. It is
essentially a window
through which the subform
shows.

You may want to
delete the label
created with the
subform window. To
This is the name of the form to which delete the label only,
select it and press
the subform control is bound. Delete.

The form footer is pushed down when the subform control is created. You
may move the footer to create more or less area at the bottom of the form.



FIGURE 7.8: Verify the link fields for the form/subform.

controlthe Sections subform bring
Select
(the white window) and
up its property sheet.

determined Access has correctly
Verify that
the link fields.

When there are more than one link
fields (i.e., the foreign key is
concatenated), separate the field
names with a semicolon. In Access
version 7.0, a builder is available to
select the field names from a list.



FIGURE 7.9: A synchronized main form/subform.

290, eightfor COMM
Note that
courses are For COMM 291, four
sections are listed in
listed in the subform. the subform.

record” navigation
Click the “next
button on the main
form to move to the
next course.

There are two sets of
navigation buttons:
one for the main form
(bottom) and one for
the subform (at the
bottom of the
subform window).



7.3.5 Non-synchronized forms itself) to make your form more attractive and easier
In this section, you will delete the link fields shown in to use.
Figure 7.8 in order to explore some of the problems In Figure 7.11, the basic form created in the previous
associated with non-synchronized forms. sections is shown and a number of shortcomings are
• Return to form design mode and delete the link identified.
fields (highlight the text and press the Delete 7.3.6.1 Changing the form’s caption
key). • Select the form as shown in Figure 7.12.
• View the form. Note that all records in the Sec- • Change its Caption property to “Courses and
tions table (not just those associated with a Sections”.
particular course) are shown.
• Attempt to add a new section to COMM 290 as 7.3.6.2 Eliminating unwanted scroll bars and
shown in Figure 7.10. navigation buttons
• Re-establish the correct link fields and save the Scroll bars and navigation buttons are also form-
form. level properties. However, in this case, you need to
modify the properties of the subform.
7.3.6 Aesthetic refinements • To quickly open the subform in design mode,
In this section, you will modify the properties of sev- double-click the subform control when viewing
eral form objects (including the properties of the form the main form in design mode (this takes some
practice)



FIGURE 7.10: A non-synchronized main form/subform.

fields for the
Delete the link

subform control
and view the
resulting form.

sections show37
Note that all
in
the subform
(moving to a
different course
has no effect).

Add a new
catalog number
and click the
record selector Since the forms are not synchronized, the
to try to save the DeptCode and CrsNum fields of the Sections
new record. table are not automatically filled in by Access.



FIGURE 7.11: A form/subform in need of some basic aesthetic refinements.

The caption of the form shows the form’s name.
A more attractive/descriptive caption is required.

Since the subform control
was automatically sized to
fit the underlying form, a
horizontal scroll bar is not
necessary.

The navigation buttons for
the subform are too easily
confused with the
navigation buttons for the
main form


7. Subforms Application to the assignment

• Bring up the property sheet for the form and scroll
FIGURE 7.12: Select the entire form.
down to change its Scroll Bars and Navigation
Button properties, as shown in Figure 7.13.
and horizontal rulerswhere in order to
Click on the square
meet
the vertical
The net result, as shown in Figure 7.14, is a more
get the property sheet for the form. attractive, less cluttered form.

• Create a form and subform for your Shipment
and ShipmentDetails information. You will
use this form to record the details of shipments
from your suppliers.
Note that both forms should be based on queries:
• the Shipment form should be based on a “sort”
query so that the most recent shipment always
shows first;
• the ShipmentDetails form should be based
on a join query so that validation information
(such as the name of the product) is shown when
a product number is entered.



• Create a form/subform to show customer orders
FIGURE 7.13: Change the scroll bars and
that have already been placed (such as the one
navigation buttons of the subform.
you entered manually in Section 4.5). The top
part of the form should contain information about
propertyScroll Bar
Set the
to “Vertical
the order plus some information about the cus-
Only” and the Navigation tomer; the subform should contain information
Buttons property to “No”. about what was ordered and what was actually
shipped.

The form you created in the preceding step is
used for viewing existing orders, not for add-
ing new orders. To add new orders, the form
must be more complex. For example, it has to
show the quantity on hand and the back
ordered quantity for each item so the user can
decide how many to ship. You will create a
form for order entry in the latter tutorials.

• Set the Allow Additions and Allow Edits proper-
ties of the “order viewing” form to No. This pre-



FIGURE 7.14: A form without subform scroll bars or navigation buttons.



vents the user from changing the details of an
order that has already been invoiced or attempt-
ing to use the form for order entry.


Access Tutorial 8: Combo Box Controls
8.1 Introduction: What is a combo
box? FIGURE 8.1: A combo box for filling in the
Activity field.
So far, the only kind of “control” you have used on
your forms has been the text box. However, Access
provides other controls (such as combo boxes, list
boxes, check boxes, radio buttons, etc.) that can be
used to improve the attractiveness and functionality
of your forms.
A combo box is list of values from which the user can
select a single value. Not only does this save typing,
it adds another means of enforcing referential integ-
rity since the user can only pick values in the combo
box. For example, a combo box for selecting course same. For example, in Figure 8.1, the combo box is
activities from a predefined list is shown in bound to the Activity field. When an item in the
Figure 8.1. combo box is selected, the string (e.g., “LEC”) is
Although advanced controls such as combo boxes copied into the underlying field exactly as if you had
and list boxes look and behave very differently than typed the letters L-E-C into a text box.
simple text boxes, their function is ultimately the


8. Combo Box Controls Learning objectives

It is important to realize that combo boxes What is tab order? How do I change it so that
have no intrinsic search capability. Combo the cursor moves in the correct order?
boxes change values—they do not automati- Should I put a combo box on a key field?
cally move to the record with the value you
select. If you want to use a combo box for 8.3 Tutorial exercises
search, you have to program the procedure
• Open your frmCourses form in design mode.
yourself (see Tutorial 15 for more details). • Ensure the toolbox and field list are visible (recall
Figure 6.3).
How do I create a bound combo box? 8.3.1 Creating a bound combo box
Can I create a combo box that displays values Although Access has a wizard that simplifies the pro-
from a different table? cess of creating combo boxes, you will start by build-
How do I show additional information in a
ing a simple combo box (similar to that shown in
Figure 8.1) with the wizard turned off. This will give
combo box?
you a better appreciation for what the wizard does
How do I prevent certain information from and provide you with the skills to make refinements
showing in the combo box? to wizard-created controls.
Can I change the order in which the items • Delete the existing Activity text box by select-
appear in a combo box? ing it and pressing the Delete key.


8. Combo Box Controls Tutorial exercises

• The wizard toggle button ( ) in the toolbox an unbound combo box, the easiest thing to
allows you to turn wizard support on and off. do is to delete it and try again.
Ensure the button is out (wizards are turned off). FIGURE 8.3: An unbound combo box (not what
• Click on the combo box tool ( ). The cursor you want).
turns into a small combo box.
• With the combo box tool selected, drag the
Activity field from the field list to the desired
location on the form’s detail section, as shown in
Figure 8.2.
The process of selecting a tool from the toolbox, and
then using the tool to drag a field from the field list
ensures that the control you create (text box, combo
box, etc.) is bound to a field in the underlying table or
query.
Since the control
is unbound, no
If you forget to drag the field in from the field field name
list, you will create an unbound combo box, as shows and the
shown in Figure 8.3. If you accidently create label is generic.



FIGURE 8.2: Create a bound combo box.

depressed. wizard button is not
Ensure the

activate the combo box tool. to
Click on the combo box button

Select the Activity field from
the field list.

have doneActivity field onname ofdetailunderlying
Drag the
this correctly, the
to the
the
area. If you

field should show in the combo box and the label
should take the value of the field’s caption



8.3.2 Filling in the combo box properties • Change the Row Source Type property to Value
In this section, you will tell Access what you want to List as shown in Figure 8.4. This tells Access to
appear in the rows of new combo box. expect a list of values in its Row Source property.
• Switch to form view and test the combo box.
FIGURE 8.4: Set the Row Source Type property.
At this point, the combo box does not show any list
items because we have not specified what the list
items should be. There are three methods of specify-
ing what shows up in the combo box list:
1. enter a list of values into the combo box’s Row
Source property;
2. tell Access to get the value from an existing table
or query;
3. tell Access to use the names of fields in an exist-
ing table (you will not use this approach).
Although the second method is the most powerful
and flexible, you will start with the first.
• Bring up the property sheet for the Activity
combo box.



• Enter the following into the Row Source property: 8.3.3 A combo box based on another
LAB;LEC;TUT table or query
• Set the Limit To List property to Yes.
An obvious limitation of the value-list method of cre-
ating combo boxes is that it is impossible to change
If the Limit To List property is set to No, the
or update the items that appear in the list without
user can ignore the choices in the combo box
and simply type in a value (e.g., “SEM”). In knowing about the Row Source property.
this particular situation, you want to limit the A more elegant and flexible method of populating the
user to the three choices given. rows of a combo box is to have Access look up the
values from an existing table or query. Although the
• Switch to form view and experiment with the basic process of setting the combo box properties
combo box. remains the same, it is more efficient to rely on the
wizard when building this type of combo box.
Notice that the combo box has some useful
Before you can continue, you need a table that con-
built-in features. For example, if you choose
tains appropriate values for course activities.
to type values rather than select them with a
mouse, the combo box anticipates your • Switch to the database window and create a new
table called Activities.
choice based on the letters you type. Thus, to
select “TUT”, you need only type “T”. • The table should consist of two fields: one called
Activity and the other called Descript, as



• Populate the table with the same values used in
FIGURE 8.5: Create a table containing course
Section 8.3.2.
activities.
The result is a table containing all the possible
course activities and a short description to explain
the meaning of the three-letter codes. You can now
return to creating a combo box based on these val-
ues.
• Delete the existing Activity combo box.
• Ensure the wizard button ( ) in the toolbox is
depressed (wizards are activated).
• Repeat the steps for creating a bound combo box
(i.e., select the combo box tool and drag the
Activity field from the field list on to the detail
section). As shown in Figure 8.6, this activates
the combo box wizard.
The wizard asks you to specify a number of things
about the combo box:
1. the table (or query) from which the combo box
values are going to be taken;



FIGURE 8.6: Create a combo box using the combo box wizard.

combo abox.
Create bound

valuesAccessa look up the
Have
from table or query.



2. the field (or fields) that you would like to show up source table or query change while the form is
as columns in the in the combo box; open these changes are not automatically
3. the width of the field(s) in the combo box (see reflected in the combo box rows. As a conse-
Figure 8.7); quence, you have to either (a) close and re-
4. the column from the combo box (if more than one open the form, or (b) requery the form.
field is showing) that is inserted into the underly- Although you can automate the requery pro-
ing field; and, cess, we will rely on the F9 key for the time
5. the label attached to the field (see Figure 8.8). being.
When you are done, the combo box should look sim-
8.3.3.1 Showing more than one field in the
ilar to that shown in Figure 8.1. However, updating or
combo box
changing the values in the combo box is much easier
when the combo box is based on a table. One problem the combo boxes created so far is that
• Add “SEM” (Seminar) to the Activities table. they are not of much use to a user who is not familiar
• Return to the form, click on the Activity combo with the abbreviations “TUT”, “SEM”, and so on. In
box, and press F9 to requery the combo box. this section, you will use the Descript field of the
• Verify that “SEM” shows up in combo box. Activities table to make the combo box more
readable, as shown in Figure 8.9.
Access creates the rows in a combo box • Delete the existing combo box and start again.
when the form is opened. If the values in the



FIGURE 8.7: Fill in the combo box
wizard dialog sheets.

morecomboone field. show
The
than
box can
Select
Activities
The new
only Activity for now.
tables contains
the values for
the combo box.

Use the column selector (the grey bar
at the top of the column) to resize the
column to the desired width.



FIGURE 8.8: Fill in the combo box wizard dialog sheets (continued).

to thecombo box is already bound
The
Activity field, this step
is automatically filled in for you.

Because the combo box is bound,
the Activity field’s caption is
provided as a default label.



tions and want them to select a course activity value
FIGURE 8.9: A combo box that shows two fields
based solely on the Descript field.
from the source table or query.
In such a case, you could include only the
Descript column in the combo box. However, this
would not work because the Activity field of the
Courses table expects a three-letter abbreviation.
As such, the combo box would generate an error
when it tried to stuff a long description into the rela-
tively short field to which it is bound.
In this section, you will create a combo box identical
to that shown in Figure 8.9 except that the key col-
umn (Activity) will be hidden from view. Despite
its invisibility, however, the Activity column will
• Fill in the wizard dialog sheets as in Section 8.3.3
still be bound to the Activity field of the underly-
but make the changes shown in Figure 8.10.
ing table and thus the combo box will work as it
• Verify that your combo box resembles Figure 8.9.
should.
8.3.3.2 Hiding the key field • Delete the existing combo box and start again
Assume for a moment that you, as a developer, do using the combo box wizard.
not want users to even see the three-letter abbrevia-



FIGURE 8.10: Use the wizard to
add more than one field to the
combo box.

Activities table into the combo box.
Bring both fields from the

resize the the “hide appropriately.
Uncheck
columns
key” box and

Note that Access version 2.0 does
not have the “hide key” feature

Select the column that provides
the value of interest (in this case,
Activity).



• Include both the Activity and Descript fields
in the combo box. FIGURE 8.12: A combo box with a hidden key.
• Resize the Activity column as shown in
Figure 8.11. Note that users of version 7.0 can
simply leave the “hide key” box checked—the
result is the same.
• Ensure that the Input Mask property for the
combo box (which is inherited from the field’s
Input Mask property) is blank.
• Verify that the resulting combo box resembles
that shown in Figure 8.12.

Combo boxes with hidden keys can be con-
8.3.3.3 Changing the order of items in the
fusing. The important thing to remember is
combo box
that even though the description (e.g., “Lec-
ture”) now shows in the combo box, what is A combo box based on a table shows the records in
really stored in the underlying field is the hid- one of two ways:
den key (e.g., “LEC”). 1. If the table does not have a primary key, the
records are shown in their natural order (that is,
in the order they were added to the database).



FIGURE 8.11: Resize the columns to hide the key.

the column selector andof
Click on the right side

drag the edge of the
Activity column to the
far left (i.e., make its width
zero)

Hiding the key is such a
common operation that
Access version 7.0 includes
the “hide key” check box.



2. If the table does have a primary key, then the If the changes are quite minor (for instance, sorting
records are sorted in ascending order according the records in a different order), you may prefer to
to the key. modify the Row Source property.
It may be, however, that you want a different order In Section 8.3.2, you set the Row Source property to
within the rows of the combo box. To achieve this, equal a list of values. When the combo box is based
you can do one of two thing: on values from a table or a query, however, the Row
1. Create a stand-alone query (in which the sort Source is an SQL statement (recall Tutorial 5) rather
order is specified) and use this query as the than a list of values. You can either edit the SQL
source for the combo box. statement directly or invoke the QBE editor.
2. Modify the “ad hoc” query within the Row Source In this section, you will order the items in you combo
property of the combo box. box according to the length of the Descript field
If you intend to make several major changes to the (this is done merely for illustrative purposes).
basic information in the underlying table (e.g., joins, • Bring up the property sheet for the Activity
calculated fields), it is usually better to create a combo box.
stand-alone query. In this way, the same query can • Put the cursor in the Row Source property. As
be used by many combo boxes. shown in Figure 8.13, a builder button ( )
appears.
• Press the builder button to enter the “SQL
builder” (i.e., the QBE editor).



(Len() is a built-in function that returns the
FIGURE 8.13: Invoke the builder for the Row
length of a string of characters).
Source property.
• Sort on DescLength in descending order.
• Switch to datasheet view to ensure the query is
working as it should.
• Ensure the Show box for the field is unchecked,
as shown in Figure 8.14.
• Instead of saving the query in the normal way,
simply close the QBE box using the close button
( ).

If you save the query, it will be added to your
collection of saved queries (the ones that are
bring up the QBEbutton to
Click the builder
editor.
displayed in the database window). However,
if you simply close the QBE window, the Row
Alternatively, you can edit
the SQL statement directly. Source property will be updated and no new
database object will be created.
• Create a calculated field called DescLength
using the following expression:
DescLength: Len([Descript])



8.3.4 Changing a form’s tab order
FIGURE 8.14: Use the QBE editor to modify the A form’s tab order determines the order in which the
Row Source property. objects on a form are visited when the Tab or Enter
(or Return) keys are pressed. Access sets the tab
order based on the order in which objects are added
to the form. As a result, when you delete a text box
and replace it with a combo box or some other con-

calleda DescLength.
Add calculated field trol, the new control becomes the last item in the tab
order regardless of its position on the form.
To illustrate the problem, you are going to create a
combo box for the DeptCode field.
• Delete the DeptCode text box and replace it with
a combo box based on the Departments table.
• Switch to form view. Notice that the focus starts
off in the CrsNum field instead of the DeptCode
field.
calculated field.
Sort on the
Uncheck the
Show box • Press tab to move from field to field. Notice that
after DeptCode is left, the focus returns to the
CrsNum field of the next record.


8. Combo Box Controls Discussion

• To fix the problem, return to form design mode For example, it never makes sense to put a combo
and select View Tab Order from the main box on a non-concatenated primary key. To illustrate
menu. this, consider the Departments form shown in
Figure 8.16. On this form, the DeptCode text box

In Access version 2.0, the menu structure is
slightly different. As such, you must select
has been replaced with a combo box that draws its
values from the Departments table.
Edit Tab Order.
FIGURE 8.16: A combo box bound to a key field.
• Perform the steps in Figure 8.15 to move Dept-
Code to the top of the tab order.

8.4 Discussion
8.4.1 Why you should never use a
combo box for a non-concatenated
key.
A mistake often made once new users learn how to This combo box appears to work. However, if you
make combo boxes is to put a combo box on every- think about it, it makes no sense: The form in
thing. There are certain situations, however, in which Figure 8.16 is a window on the Departments table.
the use of a combo box is simply incorrect. As such, when the DeptCode combo box is used,



FIGURE 8.15: Adjust the tab order of fields on a form.

selector torecord
Drag the
the selector of the field
Click on the record

desired position in you wish to move.
the list.

For forms in which the fields are arranged
in a single column from top to bottom
(such as this one), you can press Auto
Order to order them automatically.



one of two things can occur depending on whether a combo box is identical to typing “CPSC” over
new record is being created or an existing record is whatever is currently in the DeptCode field. This
being edited: causes all sorts of problems; the most obvious of
1. A new record is being created — If a new these is that by overwriting an existing value of
record is being created (i.e., a new department is DeptCode, a “duplicate value in index, primary
being added to the information system), a unique key, or relationship” error is generated (there is
value of DeptCode must be created to distin- already a department with “CPSC” as its Dept-
guish the new department from the existing Code).
departments. However, the combo box only Note that a combo box may make sense when the
shows DeptCode values of existing depart- key is concatenated. An example of this is the
ments. If the Limit To List property is set to Yes, DeptCode combo box you created in Section 8.3.4.
then the combo box prevents the user from enter-
ing a valid DeptCode value. 8.4.2 Controls and widgets
2. An existing record is being edited — It is Predefined controls are becoming increasingly popu-
important to remember that a combo box has no lar in software development. Although Microsoft
intrinsic search capability. As such, selecting includes several predefined controls with Access
“CPSC” in the DeptCode combo box does not (such as combo boxes, check boxes, radio buttons,
result in a jump to the record with “CPSC” as its etc.), a large number of more compex or specialized
key value. Rather, selecting “CPSC” from the controls are available from Microsoft and other ven-


8. Combo Box Controls Application to the assignment

dors. In addition, you can write your own custom 8.5 Application to the assignment
controls using a language like Visual C++ or Visual
There are a number of forms in your assignment that
Basic and use them in many different forms and
can be greatly enhanced by combo boxes.
applications.
• Create a combo box on your order form to allow
An example of a more complex control is the calen- the user to select customers by name rather than
dar control shown in Figure 8.17. A calendar control CustID. Since your CustID value is a counter, it
can be added to a form to make the entry of dates has no significance beyond its use as a primary
easier for the user. Microsoft calls such components key. Generally, such keys should be hidden from
“ActiveX controls” (formerly known as “OLE con- view.
trols”). Non-microsoft vendors provide similar com- • Create a combo box in your order details subform
ponents but use different names, such as “widgets”. to allow the user to select products. Since the
There are two main advantages of using controls. ProductID values are used by both you and
First, they cut down on the time it takes to develop your customers, they have some significance
an application since the controls are predefined and beyond the information system. As such, Pro-
pre-tested. Second, they are standardized so that ductID should be visible in all combo boxes. In
users encounter the same basic behavior in all appli- addition, the items in the product list should be
cations. sorted by ProductID. This makes it easier to
select a product by typing the first few numbers.
• Create combo boxes on other forms as required.


8. Combo Box Controls Application to the assignment

FIGURE 8.17: A calendar control on a form.

The calendar control can be bound
to date/time fields, thereby making
it easier for users to enter dates.

Like other objects in Access, controls have
properties and events that determine the
appearance and behavior of the control.


Access Tutorial 9: Advanced Forms
9.1 Introduction: Using calculated best course of action. However, as you will see in the
controls on forms context of subtotals, this is not always possible.

It is often useful to show summary information from
the subform on the main form. The classic example
of this is showing the subtotal from a list of order How do I create a calculated text box?
details on the main order form. What is the expression builder? When is it
In this tutorial, you are going to explore one means used?
of implementing this feature using calculated con- Where can put an intermediate result of a
trols. A calculated control is an unbound control for calculation on a form so that it does not
which the Control Source property is set to an show?
expression that Access can evaluate.
Clearly, calculated controls have a great deal in com- 9.3 Tutorial exercises
mon with the calculated query fields you created in
Section 4.3.3. Although there are no hard-and-fast 9.3.1 Creating calculated controls on
rules that dictate when to use a one over the other, forms
pushing your calculations to the lowest level (i.e., In this section, you are going to create a simple cal-
performing calculations in the query) is usually the culated text box to translate the Credits field into a
dichotomous text variable [full year,


9. Advanced Forms Tutorial exercises

half year]. Recall that you have already imple- • Test your form. Note that you are prevented from
mented this feature in Section 4.3.3.2 using a calcu- editing the calculated field. If, however, you
lated query field. change the value of Credits, the value of txt-
• Perform the steps shown in Figure 9.1 to create CourseLength changes accordingly when you
an unbound text box on your fmrCoursesMain leave the Credits field.
form.
• Set the Control Source property of the text box 9.3.2 Showing a total on the main form
using the syntax: In this section, you will create a calculated text box
= expression that displays the number of sections associated
In this case, the expression should be an “imme- with each course. The primary motivation for this
diate if” function (see Section 4.3.3.2). exercise is to illustrate some of the limitations of cal-
culated controls (as they are implemented in Access)
By default, Access interprets text in the Con-
and to provide an opportunity to explore an interest-
trol Source property field as the name of a
ing work-around.
variable (i.e., the name of a field or another
• Create a text box call txtNumSections on the
control). As such, you must remember to
main form as shown in Figure 9.2.
include the equals sign when setting this
property. The logical next step is to set the Control Source of
the field to an expression that includes the Count()
function. However, Access has a limitation in this



FIGURE 9.1: Create an unbound text box on your main form.

Credits text boxbytodragging the
Make some room
the left. tool from the box
Select the text

toolbox and click on
an appropriate space
in the detail area.

Adjust the tab order
of the fields as
necessary.

(e.g.,the label and give the textThe txt prefix is name
Edit
txtCourseLength).
box a meaningful
used
here to indicate an unbound text box.



FIGURE 9.2: Create an unbound text box to show the number of sections
associated with each course.

Sincean unbound textboundcalled txtNumSections.
Add
it is currently
box
to nothing, it is blank.

What you want
is a means of
counting the
records in the
subform and

}
displaying the
count in the
new text box.



regard: you cannot use an aggregate function 9.3.2.1 Calculating the aggregate function on
(Sum(), Avg(), Count(), etc.) on a main form that the subform
refers to a field in a subform. As a consequence, you • Create an unbound text box on the subform as
have to break the calculation into two steps: shown in Figure 9.3.
1. use the aggregate function to create a calculated • Save the subform but do not close it.
text box on the subform (i.e., a “dummy” field to • Return to the main form and set the Control
hold an intermediate result); Source of txtNumSections to equal the value
2. create a calculated control on the main form that of txtNumSectionsOnSub. Since the naming
references the dummy text box created in the first conventions for objects on forms and subforms
step. can be tricky, use the expression builder (as
shown in Figure 9.4) to build the name for you.
It is important that you realize that this proce- The expression builder organizes all the elements of
dure does not involve any immutable, funda- the database environment into a hierarchical struc-
mental information systems knowledge. ture. You build an expression by “drilling down” to the
Rather, it is merely an example of the type of element you need and double-clicking to copy its
work-around (hack, kludge, etc.) that is rou- name into the text area.
tinely used when using a tool like Access to
create a custom application. The expression builder takes some practice.
One problem is that it is easy to double-click



FIGURE 9.3: Perform the count on the subform.

txtNumSectionsOnSub and place it in the form header
Create a calculate control called
(do not worry about its location, you will move it later).

propertyControl Source
Set the
to
=Count([Section]).
Note that any field can be
used as the argument for the
Count() function.



FIGURE 9.4: Use the builder to drill down to the calculated control on the subform.

Controlthe builder from the drill
Invoke
Source property and
down to the calculated control you
just created on the subform.
Note that when the main
form and the subform are
both open, the subform
appears twice in the builder:
once as a “stand-alone”
form (under “Loaded
Forms”) and once as a
component of the main form
(press the + sign on the
frmCoursesMain
folder). You want to use the
latter (you will never
access the subform in stand-
alone mode).



on the wrong thing. Another problem is that • Test the form. The value of txtNumSections
Access attempts to guide you by inserting and txtNumSectionsOnSub should be identi-
«Expr» place-holders all over the place. The cal, as shown in Figure 9.5.
solution to both problems is to click on the text FIGURE 9.5: The number of sections on the main
window and make liberal use of the Delete form.
key.

The point made about “stand-alone” and
“component” subforms in Figure 9.4 is
extremely important. The reason you use the
sfrm prefix is so you know that the form is
designed to be a component of another form.
If you select the stand-alone version the form
in the builder, the name created by the builder
The “dummy” text box is visible in
will be incorrect and an error will result. the subform. Although you will
eventually hide it, it is useful to
• Close the subform (in version 7.0 and 8.0, the display it until you know both steps
main form and subform cannot be open at the of the calculation are working
properly.
same time).


9. Advanced Forms Discussion

9.3.2.2 Hiding the text box on the subform • Drag (or cut and paste) txtNumSectionsOn-
The obvious problem in Figure 9.5 is that the dummy Sub from the form header to the page header, as
text box shows on the subform. There are at least shown in Figure 9.6.
two ways to get around this: one is to set the Visible • Test the result.
property of the text box to No; a slightly more elegant
approach is to use the page header or page footer 9.4 Discussion
to hide the text box. In Section 4.3.3.2 and Section 9.3.1, you accom-
The page header and footer are areas on the form plished the same thing (showing half year or
that only show when the form is printed. Since you full year) using different techniques. The advan-
will never print a form (reports are used for printed tage of implementing this as a calculated query field
material), these areas can be used to hide intermedi- is that you can use this field repeatedly in other
ate results, etc. forms. On the other hand, if you do the transforma-
• In design mode, select View Page Header/ tion on the form, you have to repeat the calculation
Footer from the menu. on every form that requires the calculated field.
In the case of the aggregate function, the situation is

In version 2.0, the menu structure is slightly
different. As such, you must select Format
slightly different. Although you can use the totals
feature of QBE (see on-line help) to count the num-
Page Header/Footer. ber of sections for a particular course within a query,
the resulting recordset is non-updatable (and hence


9. Advanced Forms Discussion

FIGURE 9.6: Hide the intermediate result in the page header.

menu (Format Page Header/Footer fromversion
Select View
Page Header/Footer in
the
the field you and paste)
Drag (or cut
want to hide
2.0) to show the page header and footer. into the page header.


9. Advanced Forms Application to the assignment

not much use for editing course names, etc.). As a
result, you are forced to do the calculation on the
form rather than in the query.

To show the subtotal, tax, and grand total on your
order form, you use the same techniques illustrated
here. The only difference is that you use the Sum()
function instead of the Count() function to get the
subtotal for the order.
• Create a dummy field on your OrderDetails
subform to calculate the subtotal for the order.
• Calculate the tax (G.S.T. only for wholesale) and
grand total on the main form (traditionally, this
information is located near the bottom of the
form—but not in the form footer).


Access Tutorial 10: Parameter Queries
The last few tutorials have been primarily concerned result is that parameters can be used to create
with interface issues. In the remaining tutorials, the extremely flexible queries.
focus shifts to transaction processing. When the concepts from this tutorial are combined
with action queries (Tutorial 11) and triggers
10.1 Introduction: Dynamic queries (Tutorial 13), you will have a the skills required to
using parameters create a simple transaction processing system with-
A parameter query is a query in which the criteria out writing a line of programming code.
for selecting records are determined when the query
is executed rather than when the query is designed. 10.2 Learning objectives
For example, recall the select query shown in What is a parameter query? How do I create
Figure 4.6. In this query, the results set is limited to one?
records that satisfy the criterion DeptCode = How do I prompt the user to enter parameter
“COMM”. If you wanted a different set of results, you values?
would have to edit the query (e.g., change the crite-
rion to “CPSC”) and rerun the query.
How do I create a query whose results
depend on a value on a form?
However, if a variable (parameter) is used for the cri-
terion, Access will prompt the user for the value of
the variable before executing the query. The net


10. Parameter Queries Tutorial exercises

10.3 Tutorial exercises attempts to bind the variable to some value. To do
this, it performs the following tests:
10.3.1 Simple parameter queries 1. First, Access checks whether the variable is the
• If you do not already have a qryCourses query name of a field or a calculated field in the query. If
like the one shown in Figure 4.6, create one now it is, the variable is bound to the current value of
and save it under the name pqryCourses. the field. For example, if the parameter is named
• Replace the literal string in the criteria row [DeptCode], Access replaces it with the current
(“COMM”) with a variable ([X]). value of the DeptCode field. Since X is not the
name of a field or a calculated field in this particu-
By default, Access expects criteria to be literal lar query, this test fails.
strings of text. As a result, it automatically 2. Second, Access attempts to resolve the parame-
adds quotation marks to text entered in the ter as a reference to something within the current
criteria row. To get around this, place your environment (e.g., the value on an open form).
parameter names inside of square brackets. Since there is nothing called X in the current envi-
ronment, this test fails.
• Execute the query as shown in Figure 10.1. 3. As a last resort, Access asks the user for the
When Access encounters a variable (i.e., something value of the parameter via the “Enter Parameter
that is not a literal string) during execution, it Value” dialog box.



FIGURE 10.1: Convert a select query into a parameter query.

(herethe queryisand supply the value of value
Run
Access asking for
a parameter
X).

(“COMM”) with a parameter (X)
Replace the literal criterion



Note that the spelling mistakes discussed in may be useful to be able to generate a list of courses
Section 4.3.4 are processed by Access as offered by the department currently being viewed.
parameters. Although you could use a creatively-named parame-
ter to invoke the “Enter Parameter Value” dialog, this
10.3.2 Using parameters to generate requires the user to type in the value of DeptCode.
prompts A more elegant approach is to have Access pull the
Since the name of the parameter can be anything value of a parameter directly from the open form.
(as long as it is enclosed in square brackets), you This exploits the second step in the operation of a
can exploit this feature to create quick and easy dia- parameter query (Access will attempt to resolve a
log boxes. parameter with the value of an object within the cur-
• Change the name of your DeptCode parameter rent environment). The basic idea is shown in
from [X] to [Courses for which depart- Figure 10.3.
ment?]. The key to making this work is to provide a parame-
• Run the query, as shown in Figure 10.2. ter name that correctly references the form object in
which you are interested. In order to avoid having to
10.3.3 Values on forms as parameters remember the complex naming syntax for objects on
A common requirement is to use the value on a form forms, you can invoke the expression builder to
to influence the outcome of a query. For instance, if select the correct name from the hierarchy of data-
the user is viewing information about departments, it base objects.



FIGURE 10.2: Select a parameter name that generates a useful prompt.

the value of the for
When Access asks

parameter, it uses the
parameter’s name.

Only records that satisfy
the criteria are included
in the results set.

for which department?].
Name the parameter [Courses



FIGURE 10.3: Using the value on an open form as a parameter in a query.

The current value in the DeptCode field on
the form is used as a parameter in the query.


10. Parameter Queries Application to the assignment

• Create a very simple form based on the Although the naming syntax of objects in
Departments table and save it as frmDepart- Access is tricky, it is not impossible to com-
ments. prehend. For example, the name
• Leave the form open (in form view or design Forms![frmDepartments]![DeptCode]
mode, it does not matter). consists of the following elements: Forms
• Open pqryCourses in design mode, place the refers to a collection of Form objects; [frm-
cursor in the criteria row of the DeptCode field, Departments] is a specific instance of a
and invoke the expression builder as shown in Form object in the Forms collection; [Dept-
Figure 10.4. Code] is a Control belonging to the form. See
• Perform the steps shown in Figure 10.5 to create Tutorial 14 for more information on the hierar-
a parameter that references the DeptCode field chy of objects used by Access.
on the frmDepartments form.
• Run the query. The results set should correspond 10.4 Application to the assignment
to the department showing in the frmDepart- You will use parameter queries as the basis for sev-
ments form. eral action queries (see Tutorial 11) that process
• Move to a new record on the form. Notice that transactions against master tables. For now, simply
you have to requery the form (Shift-F9) in order create the parameter queries that take their criteria
for the new parameter value to be used (see values from forms you have already created.
Figure 10.6).



FIGURE 10.4: Invoke the builder to build a parameter.

Criteria row of the the
Place the cursor in
DeptCode field and
right-click to bring up
the pop-up menu.

Departmentsform basedleavetheopen
Create a simple
table and
on
it
in the background.

Select Build to
invoke the builder.



FIGURE 10.5: Use the builder to select the name of the object you want to use as a parameter.

aDouble-click DeptCode toarea, delete the text,area.tryyou make
mistake, move to the text
move it to the text
and
If
again.

the forms in yourget a list of all
Select Forms to
database.

form isthe frmDepartments
Since
open, click on Loaded
Forms and select the form.

Press OK
when done.
Move to the middle pane and
select Field List to get a list of the
The text will
be copied
fields on the form in the pane on into the
the far right. criteria row.



FIGURE 10.6: Requery the results set to reflect changes on the form.

form. Notice that the query is not
Move to a new record on the

automatically updated.

parameter valueto(MATH in this case)
Press Shift-F9 requery. The new

is used to select records.



• Create a parameter query to show all the order • It shows the change (positive or negative but not
details for a particular order. zero) in backorders for each item in a particular
• Create a second parameter query to show all the order.
shipment details for a particular shipment. • The query consist of three fields: OrderID, Pro-
Each order may result in a number of changes being ductID and a calculated field Qty (i.e., the
made to the BackOrders table. For some items in change in the back order for a particular product).
the order, more product is ordered than is actually • The name of the parameter is in this query is sim-
shipped (i.e., a backorder is created). For other ply[pOrderID]. Since the value of this parame-
items, more product is shipped than is ordered (i.e., ter will be set by the Visual Basic shortcut before
a backorder is filled). the query is run, there is no need to set it to a
value on a form.
In Tutorial 15, you are supplied with a “shortcut”
Visual Basic procedure that makes the changes to Since the query is accessed by a program,
the BackOrders table for you. However, the short- the name of the query and all the fields must
cut procedure requires a query that lists the changes be exactly as described above. In other
that must be made to the BackOrders table for a words, you are given a precise specification
particular order. The requirements for this query are for a database object that fills a role in a pro-
the following: cess designed and implemented by someone
• The name of the query is else. You will not understand how the query
pqryItemsToBackOrder fits in until Tutorial 15.


Access Tutorial 11: Action Queries
11.1 Introduction: Queries that 2. Append — similar to a make-table query, except
change data that the results set of the query is appended to an
existing table;
11.1.1 What is an action query? 3. Update — allows the values of one or more fields
in the result set to be modified; and,
All of the queries that you have created to this point
4. Delete — deletes all the records in the results set
have been variations of “select” queries. Select que-
from the underlying table.
ries are used to display data but do not actually
change the data in any way. Since the operation of all four types of action queries
is similar, we will focus on update queries in this tuto-
Action queries, in contrast, are used to change the
rial.
data in existing tables or make new tables based on
the query's results set. The primary advantage of
11.1.2 Why use action queries?
action queries is that they allow you to modify a large
To motivate the examples in the first part of this tuto-
number of records without having to write Visual
rial, we are going to assume that the number of cred-
Basic programs.
its allocated to courses in certain departments need
Access provides four different types of action que-
to be changed. For example, assume that you need
ries: to increase the number of credits for courses in the
1. Make table — creates a new table based on the Commerce department by 1.5 times their current val-
results set of the query;


11. Action Queries Learning objectives

ues. There are at least four different ways of accom- 3. Write a Visual Basic program to automate Step 2.
plishing this task: This is a good approach; however, it clearly
1. Create a calculated field called NewCredits that requires the ability to write Visual Basic pro-
multiplies the value of Credits by 1.5 — The grams.
query containing the calculated field can be used 4. Create an update query that (a) selects only
in place of the Courses table whenever credit those courses that require modification and (b)
information is required. Of course, the values replaces the value of Credits with Credits *
stored in the Courses table are still the old val- 1.5. — This approach is computationally efficient
ues. Although there might be some advantages and allows you to work with the QBE editor rather
to keeping the old values, it may cause confusion than a programming language.
about which values to use. In addition, the use of
a calculated field creates a computational load 11.2 Learning objectives
that becomes larger as the number of courses What is an action query? Why would I want to
increases. use one?
2. Go through the Courses table record by record
and manually change all the values — This
How do I make a backup copy of one of my
tables?
approach is tedious and error prone. Further-
more, it is simply impractical if the number of How to I undo (rollback) an action query once
courses is large. I have executed it?


11. Action Queries Tutorial exercises

How do I update only certain records in a • While still in query design mode, select Query
table? Make Table from the main menu and provide a
How do I create a button on a form? How do I name for the target table (e.g., CoursesBackup)
make an action query execute when the as shown in Figure 11.1.
button is pressed? • Select Query Run from the main menu to exe-
cute the action query, as shown in Figure 11.2.
11.3 Tutorial exercises Action queries do not execute until you explic-
itly run them. Switching to datasheet mode
11.3.1 Using a make-table query to create only provides a preview of the results set.
a backup
Since action queries permanently modify the data in • Save the query. If you switch to the database win-
tables, it is a good idea to create a backup of the dow, you will notice that the new make-table
table in question before running the query. An easy query has a different icon than the select queries.
way to do this is to use a make-table query.
• Create a select query based on the Courses 11.3.2 Using an update query to rollback
table and save it as qryCoursesBackup. changes
• Project the asterisk (*) into the query definition so Having a backup table is not much use without a
that all the fields are included in the results set. means of using it to restore the data in your original
table. In this section, you will use an update query to



FIGURE 11.1: Use a make-table query to back up and existing table

aTransform the Select query into
Make Table query

Provide a name for the new
(target) table.

the query definition.into
Project all fields (*)



FIGURE 11.2: Run the make-table query.

You can switch to datasheet mode to view the results
set. Note that this does not actually execute the query.

Query Run. query, you must select
To execute the
Alternatively, you can
press the “run” (!) icon on the toolbar.

The warning box reminds you that you
are about to make permanent changes
to the data in the database.



replace some of the values in your Courses table
FIGURE 11.3: Create an ad hoc relationship
with values from your CoursesBackup table.
between the table and its backup.
• Create a new query based on the Courses and
CoursesBackup tables.
• Since no relationship exists between these
tables, create an ad hoc relationship within the
query as shown in Figure 11.3.
• Select Query Update from the main menu. Note
that this results in the addition of an Update To
row in the query definition grid.
• Project Credits into the query definition and fill
in the Update To row as shown in Figure 11.4.
• Save the query as qryRollbackCredits.
Now is a good point to stop and interpret what you counterparts in thethe key on to their
Drag the fields in
backup table.
have done so far:
1. By creating a relationship between the Courses You cannot drag two fields at once or
table and its backup, you are joining together the enforce referential integrity in a QBE
relationship like you can in the main
records from both tables that satisfy the condi- relationship editor.



tion:
FIGURE 11.4: Fill in the Update To field.
Courses.DeptCode =
CoursesBackup.DeptCode AND
the query an update query. make
Select Query Update to
Courses.CrsNum =
CoursesBackup.CrsNum.
2. By projecting Courses.Credits into the query,
you are making it the target for the update. In
other words, the values in Courses.Credits
are going to be modified by the update action.
3. By setting the Update To field to Courses-
Backup.Credits, you are telling Access to
replace the contents of Courses.Credits with
the contents of CoursesBackup.Credits.
Whenever this query is run, it will replace whatever is
in the Credits field of all the records in the
Courses table with values from the backup. You will
use this query to “rollback” updates made later on.

syntax totable name.field name
Use the
disambiguate the field name.



11.3.3 Using an update query to make
FIGURE 11.5: Create an update query that
selective changes updates a subset of the records.
Now that you have an infrastructure for undoing any
errors, you can continue with the task of updating
credits for the Commerce department.
• Create an update query based on the Courses
table and save it as qryUpdateCredits.
To fieldUpdate
Set the
to replace
Credits with
• Set the Update To field to [Courses]*1.5. Credits × 1.5
Note that if you do not include the square brack-
ets, Access will interpret Courses as a literal
string rather than a field name.

Since this particular query only contains one
table, the table name.field name
syntax is not required for specifying the
Update To expression.

• Since you only want to apply the change to Com- the update. Note limitDeptCodeofis
Add a criteria to
that
the scope
merce courses, enter a criterion for the Dept- not changed in any way by this query.
Code field, as shown in Figure 11.5.



• Run the query and verify that update has been 11.3.5 Attaching action queries to
performed successfully. buttons
As a designer, you should not expect your users to
11.3.4 Rolling back the changes understand your query naming convention, rum-
While testing the qryUpdateCredits query, your mage through the queries listed in the database win-
exuberance may have led you to execute it more dow, and execute the queries that need to be
than once. To return the Courses table to its state executed. As such, it is often useful to create buttons
before any updates, all you need to do it run your on forms and “attach” the action queries to the but-
rollback query. tons. When the button is pressed, the query is exe-
• Run qryRollback credits by double-clicking its cuted.
icon in the database window.
Although we have not yet discussed buttons (or
Once an action query is created, it has more events in general), the button wizard makes the cre-
in common with subroutines written in Visual ation of this type of form object straightforward.
Basic than standard select queries. As such, it • Modify qryUpdateCredits so that it updates
is best to think of action queries in terms of only those departments matching the DeptCode
procedures to be executed rather than virtual value in the frmDepartments table (see
tables or views. Double-clicking an action Figure 11.6).
query executes it. • Save the resulting action parameter query as
pqryUpdateCredits and close it.



FIGURE 11.6: Create an action parameter query to update Credits for a particular department.

specifies theoperation
The update
action to update to those records scope of the
The criterion limits the
matching
perform on the records. the current parameter value


11. Action Queries Application to the assignment

• Switch to the design view of frmDepartments • Create backup copies of your Products and
and add a button as shown in Figure 11.7. BackOrders tables using make-tables queries.
• Attach the pqryUpdateCredits query to the Save these queries but note that they only need
button as shown in Figure 11.8. to be run once.
• Provide a caption and a name for the button as • Create a rollback query that allows you to return
shown in Figure 11.9. your Products table to its original state.
• Switch to form view. Press the button to run the Rolling back the BackOrders table is more complex
query (alternatively, use the shortcut key by than rolling back the Products table. This is
pressing Alt-U) as shown in Figure 11.10. because we are making the assumption that no
products are ever added or deleted to the system. As
11.4 Application to the assignment such, all the information needed for the rollback is in
the backup copy of Products.
11.4.1 Rolling back your master tables
In contrast, records are added to the BackOrders
As you begin to implement the transaction process- table on a regular basis. As a result, the Back-
ing component of your system, it is worthwhile to Orders table and its backup may contain a different
have a means of returning your master tables to their number of records. If so, the match-and-replace pro-
original state (i.e., their state when you started devel- cess used for rolling back Products is inappropri-
oping the system). ate.



FIGURE 11.7: Add a button to the form using the button wizard.

thethere is insufficient space fortoa the rightdrag
If
border of the detail section
button,

wizard button in the
Ensure that the

toolbox is
depressed (wizards
are activated).

Select the “command button” tool and click
on an appropriate location on the form detail
section. The button wizard should appear



FIGURE 11.8: Use the wizard to attach an action query to the button.

perform can bedifferentto
Buttons
many
created
actions
in Access. The button wizard
organizes these actions into
categories. Select
Miscellaneous Run Query.

queries (including non-action queries).
The wizard lists all the available
Select pqryUpdateCredits.



FIGURE 11.9: Use the wizard to attach a query to a button (continued)

You can show either a picture (icon) or a caption
on the button. Enter a suitable caption.
Including an ampersand () in
the caption creates a shortcut
key from the letter immediately
following the ampersand.
Shortcut keys can be invoked
using the Alt-letter
combination (the letter is
underlined). In this case, Alt-U
moves the focus directly to the
button.

button. The cmd prefixname for the
Provide a meaningful
indicates a
command button.



FIGURE 11.10: Execute the action query by pressing the button.

(or press Alt-U to use the shortcut). query
Press the button to execute the action



The easiest way to rollback the BackOrders table is ries. These queries will allow you to perform
to delete all the records it contains and use an reasonably complex transaction processing opera-
append query to replace the records from the tions on your master tables.
backup. • Create an update query to add all products in a
• Open your BackOrders table in datasheet mode shipment to inventory.
and select Edit Select All Records from the
menu (alternatively, press Control-A) Note that this query should only process ship-
• Press the Delete key. ment details for the current shipment (i.e., it
• Create an append query that adds the records should be based on a parameter query similar
in the backup table to the BackOrders table. to the one you created in Section 10.4).
Once you learn the Access macro language or • Create a button on the shipments form to perform
Visual Basic for Applications, you will be able to write this update.
a small procedure to execute these steps for you. • Create an update query to subtract items from
For the assignment, however, this “manual rollback” inventory when you process an order from your
is sufficient. customers. Do not attach this query to a button at
this point.
11.4.2 Processing transactions
You are now in a position to combine parameter que- This query should only process order details
ries and action queries into parameter-action que- from the current order.


Access Tutorial 12: An Introduction to Visual Basic
12.1 Introduction: Learning the simple programs we are writing here, these
basics of programming terms are interchangeable.

Programming can be an enormously complex and 12.1.1 Interacting with the interpreter
difficult activity. Or it can be quite straightforward. In
Access provides two ways of interacting with the
either case, the basic programming concepts remain
VBA language. The most useful of these is through
the same. This tutorial is an introduction to a handful
saved modules that contain VBA procedures. These
of programming constructs that apply to any “third
procedures (subroutines and functions) can be run to
generation” language, not only Visual Basic for
do interesting things like process transactions
Applications (VBA).
against master tables, provide sophisticated error
Strictly speaking, the language that is checking, and so on.
included with Access is not Visual Basic—it is The second way to interact with VBA is directly
a subset of the full, stand-alone Visual Basic through the interpreter. Interpreted languages are
language (which Microsoft sells separately). easier to experiment with since you can invoke the
In Access version 2.0, the subset is called interpreter at any time, type in a command, and
“Access Basic”. In version 7.0, it is slightly watch it execute. In the first part of this tutorial, you
enlarged subset called “Visual Basic for Appli- are going to invoke Access’ VBA interpreter and exe-
cations” (VBA). However, in the context of the cute some very simple statements.


12. An Introduction to Visual Basic Learning objectives

In the second part of the tutorial, you are going to 12.3 Tutorial exercises
create a couple of VBA modules to explore looping,
conditional branching, and parameter passing. 12.3.1 Invoking the interpreter
• Click on the module tab in the database window
12.2 Learning objectives and press New.
What is the debug/immediate window? How This opens the module window which we will use in
do I invoke it? Section 12.3.3. You have to have a module window
What are statements, variables, the open in order for the debug window to be available
assignment operator, and predefined from the menu.
functions? • Select View Debug Window from the main
How do I create a module containing VBA menu. Note that Control-G can be used in ver-
sion 7.0 and above as a shortcut to bring up the
code?

debug window.
What are looping and conditional branching?

What language constructs can I use to In version 2.0, the “debug” window is called
implement them? the “immediate” window. As such, you have to
How do I use the debugger in Access? use View Immediate Window. The term

What is the difference between an interpreted
debug window will be used throughout this
tutorial.
and compiled programming language?


12. An Introduction to Visual Basic Tutorial exercises

12.3.2 Basic programming constructs 12.3.2.2 Variables and assignment
In this section, we are going to use the debug win- A variable is space in memory to which you assign a
dow to explore some basic programming constructs. name. When you use the variable name in expres-
sions, the programming language replaces the vari-
12.3.2.1 Statements
able name with the contents of the space in memory
Statements are special keywords in a programming at that particular instant.
language that do something when executed. For • Type the following:
example, the Print statement in VBA prints an s = “Hello”↵
expression on the screen. ? s “ world”↵
• In the debug window, type the following: ? “s” “ world”↵
Print “Hello world!”↵
In the first statement, a variable s is created and the
(the ↵ symbol at the end of a line means “press the string Hello is assigned to it. Recall the function of
Return or Enter key”). the concatenation operator () from Section 4.4.2.
In VBA (as in all dialects of BASIC), the ques- Contrary to the practice in languages like C
tion mark (?) is typically used as shorthand for and Pascal, the equals sign (=) is used to
the Print statement. As such, the statement: assign values to variables. It is also used as
? “Hello world!”↵ is identical to the the equivalence operator (e.g., does x = y?).
statement above.



When the second statement is executed, VBA recog- is a function that is provided as part of the program-
nizes that s is a variable, not a string (since it is not ming environment.
in quotations marks). The interpreter replaces s with For example, cos(x) is a predefined function in
its value (Hello) before executing the Print com- many computer languages—it takes some number x
mand. In the final statement, s is in quotation marks as an argument, does some processing to find its
so it is interpreted as a literal string. cosine, and returns the answer. Note that since this
function is predefined, you do not have to know any-
Within the debug window, any string of char-
thing about the algorithm used to find the cosine, you
acters in quotations marks (e.g., “COMM”) is
just have to know the following:
interpreted as a literal string. Any string with-
out quotation marks (e.g., COMM) is interpreted 1. what to supply as inputs (e.g., a valid numeric
as a variable (or a field name, if appropriate). expression representing an angle in radians),
Note, however, that this convention is not uni- 2. what to expect as output (e.g., a real number
versally true within different parts of Access. between -1.0 and 1.0).

12.3.2.3 Predefined functions The on-line help system provides these two
pieces of information (plus a usage example
In computer programming, a function is a small pro-
and some additional remarks) for all VBA pre-
gram that takes one or more arguments (or param-
defined functions.
eters) as input, does some processing, and returns
a value as output. A predefined (or built-in) function



In this section, we are going to explore some basic
FIGURE 12.1: Interacting with the Visual Basic
predefined functions for working with numbers and
interpreter.
text. The results of these exercises are shown in
Figure 12.1.
• Print the cosine of 2π radians:
pi = 3.14159↵
? cos(2*pi)↵ The argument contains
• Convert a string of characters to uppercase: an expression.
s = “basic or cobol”↵
? UCase(s)↵ UCase() converts a
string to uppercase.
• Extract the middle six characters from a string
starting at the fifth character:
? mid (s,5,6)↵ Mid() extracts
characters from the
12.3.2.4 Remark statements string defined earlier.
When creating large programs, it is considered good
programming practice to include adequate internal
documentation—that is, to include comments to
explain what the program is doing.



Comment lines are ignored by the interpreter when
FIGURE 12.2: The declarations page of a Visual
the program is run. To designate a comment in VBA,
Basic module.
use an apostrophe to start the comment, e.g.:
‘ This is a comment line!
Print “Hello” ‘the comment starts
here
The original REM (remark) statement from BASIC
can also be used, but is less common.
REM This is also a comment (remark)

12.3.3 Creating a module
strings are compared (e.g., does uppercase/ lower-
• Close the debug window so that the declaration
case matter?). The Option Explicit statement
page of the new module created in
forces you to declare all your variables before using
Section 12.3.3 is visible (see Figure 12.2). them.
The two lines:
Option Compare Database
Option Explicit In version 2.0, Access does not add the
Option Explicit statement by default. As
are included in the module by default. The Option such you should add it yourself.
Compare statement specifies the way in which



A module contains a declaration page and one or 12.3.4 Creating subroutines with looping
more pages containing subroutines or user-defined and branching
functions. The primary difference between subrou- In this section, you will explore two of the most pow-
tines and functions is that subroutines simply exe-
erful constructs in computer programming: looping
cute whereas functions are expected to return a and conditional branching.
value (e.g., cos()). Since only one subroutine or
• Create a new subroutine by typing the following
function shows in the window at a time, you must anywhere on the declarations page:
use the Page Up and Page Down keys to navigate
Sub LoopingTest()↵
the module.
Notice that Access creates a new page in the mod-

The VBA editor in version 8.0 has a number of ule for the subroutine, as shown in Figure 12.3.
enhancements over earlier version, including 12.3.4.1 Declaring variables
the capability of showing multiple functions
When you declare a variable, you tell the program-
and subroutines on the same page.
ming environment to reserve some space in memory
for the variable. Since the amount of space that is
required is completely dependent on the type of data
the variable is going to contain (e.g., string, integer,
Boolean, double-precision floating-point, etc.), you



• Save the module as basTesting.
FIGURE 12.3: Create a new subroutine. One of the most useful looping constructs is For
condition... Next. All statements between
the For and Next parts are repeated as long as the
condition part is true. The index i is automati-
cally incremented after each iteration.
• Enter the remainder of the LoopingTest pro-
You can use the procedure gram:
combo box to switch between
procedures in a module. s = “Loop number: ”
For i = 1 To 10
have to include data type information in the declara- Debug.Print s i
tion statement. Next i
• Save the module.
In VBA, you use the Dim statement to declare vari-
ables. It is customary in most programming lan-
• Type the following into the space between the guages to use the Tab key to indent the ele-
Sub... End Sub pair: ments within a loop slightly. This makes the
Dim i as integer program more readable.
Dim s as string



Note that the Print statement within the subroutine
FIGURE 12.4: Run the LoopingTest
is prefaced by Debug. This is due to the object-ori-
subroutine in the debug window.
ented nature of VBA which will be explored in greater
detail in Tutorial 14.
12.3.4.2 Running the subroutine
Now that you have created a subroutine, you need to
run it to see that it works. To invoke a subroutine, you
simply use its name like you would any statement.
• Select View Debug Window from the menu (or
press Control-G in version 7.0).
• Type: LoopingTest↵ in the debug window, as
12.3.4.3 Conditional branching
We can use a different looping construct, Do Until
condition... Loop, and the conditional
branching construct, If condition Then...
Else, to achieve the same result.
by typing its name in the debug window.
Invoke the LoopingTest subroutine



• Type the following anywhere under the End Sub Loop
statement in order to create a new page in the • Run the program
module:
Sub BranchingTest↵ 12.3.5 Using the debugger
• Enter the following program: Access provides a rudimentary debugger to help you
Dim i As Integer step through your programs and understand how
Dim s As String they are executing. The two basic elements of the
Dim intDone As Integer debugger used here are breakpoints and stepping
s = “Loop number: “ (line-by-line execution).
i = 1 • Move to the s = “Loop number: ” line in your
intDone = False BranchingTest subroutine and select Run
Do Until intDone = True Toggle Breakpoint from the menu (you can also
If i 10 Then press F9 to toggle the breakpoint on a particular
Debug.Print “All done” line of code).
intDone = True Note that the line becomes highlighted, indicating the
Else presence of an active breakpoint. When the program
Debug.Print s i runs, it will suspend execution at this breakpoint and
i = i + 1 pass control of the program back to you.
End If



• Run the subroutine from the debug window, as
FIGURE 12.5: Execution of the subroutine is
suspended at the breakpoint.
• Step through a couple of lines in the program
line-by-line by pressing F8.
By stepping through a program line by line, you can
usually find any program bugs. In addition, you can
use the debug window to examine the value of vari-
ables while the program’s execution is suspended.
• click on the debug window and type
? i↵
to see the current value of the variable i.

12.3.6 Passing parameters
In the BranchingTest subroutine, the loop starts The outlined box indicates the
current location of the
at 1 and repeats until the counter i reaches 10. It interpreter in the program. Press
may be preferable, however, to set the start and fin- F8 to execute the line of code.
ish quantities when the subroutine is called from the
debug window. To achieve this, we have to pass
parameters (or arguments) to the subroutine.



The main difference between passed parameters
FIGURE 12.6: Highlight the code to copy it.
and other variables in a procedure is that passed
parameters are declared in the first line of the sub-
routine definition. For example, following subroutine
declaration
Sub BranchingTest(intStart as
Integer, intStop as Integer)
not only declares the variables intStart and
intStop as integers, it also tells the subroutine to
expect these two numbers to be passed as parame-
ters.
To see how this works, create a new subroutine
called ParameterTest based on Branch-
ingTest.
• Type the declaration statement above to create
the ParameterTest subroutine.
• Switch back to BranchingTest and highlight all
the code except the Sub and End Sub state-
ments, as shown in Figure 12.6.



• Copy the highlighted code to the clipboard (Con- 12.3.7 Creating the Min() function
trol-Insert), switch to ParameterTest, and In this section, you are going to create a user-
paste the code (Shift-Insert) into the Parame- defined function that returns the minimum of two
terTest procedure. numbers. Although most languages supply such a
To incorporate the parameters into ParameterT- function, Access does not (the Min() and Max()
est, you will have to make the following modifica- function in Access are for use within SQL statements
tions to the pasted code: only).
• Replace i = 1 with i = intStart. • Create a new module called basUtilities.
• Replace i 10 with i intStop. • Type the following to create a new function:
• Call the subroutine from the debug window by Function MinValue(n1 as Single, n2
typing: as Single) as Single↵
ParameterTest 4, 12↵ This defines a function called MinValue that returns
a single-precision number. The function requires two
If you prefer enclosing parameters in brack-
single-precision numbers as parameters.
ets, you have to use the Call sub
name(parameter1, ..., parametern) Since a function returns a value, the data type
syntax. For example: of the return value should be specified in the
Call ParameterTest(4,12)↵ function declaration. As such, the basic syn-
tax of a function declaration is:


12. An Introduction to Visual Basic Discussion

Function function 12.4 Discussion
name(parameter1 As data type,
…, parametern As data type) As 12.4.1 Interpreted and compiled
data type languages
The function returns a variable named
VBA is an interpreted language. In interpreted lan-
function name.
guages, each line of the program is interpreted (con-
• Type the following as the body of the function: verted into machine language) and executed when
the program is run. Other languages (such as C,
If n1 = n2 Then
Pascal, FORTRAN, etc.) are compiled, meaning
MinValue = n1
that the original (source) program is translated and
Else
saved into a file of machine language commands.
MinValue = n2
This executable file is run instead of the source
End If
code.
• Test the function, as shown in Figure 12.7.
Predictably, compiled languages run much faster
then interpreted languages (e.g., compiled C++ is
generally ten times faster than interpreted Java).
However, interpreted languages are typically easier
to learn and experiment with.


12. An Introduction to Visual Basic Discussion

FIGURE 12.7: Testing the MinValue() function.

function using conditional branching.
Implement the MinValue()

various parameterby passing it
Test the function
values.

According to the function
declaration, MinValue()
expects two single-precision
numbers as parameters.
Anything else generates an error.

These five lines could be replaced with one line:
MinValue = iif(n1 = n2, n1, n2)


12. An Introduction to Visual Basic Application to the assignment

You will need a MinValue() function later in the
assignment when you have to determine the quantity
to ship.
• Create a basUtilities module in your assign-
ment database and implement a MinValue()
function.

To ensure that no confusion arises between
your user-defined function and the built-in
SQL Min() function, do not call you function
Min().


Access Tutorial 13: Event-Driven Programming
Using Macros
13.1 Introduction: What is event- the order entry is complete, the inventory update
driven programming? module is executed, and so on.
Event-driven programming, graphical user interfaces
In conventional programming, the sequence of oper-
ations for an application is determined by a central (GUIs), and object-orientation are all related since
forms (like those created in Tutorial 6) and the
controlling program (e.g., a main procedure). In
graphical interface objects on the forms serve as the
event-driven programming, the sequence of opera-
skeleton for the entire application. To create an
tions for an application is determined by the user’s
event-driven application, the programmer creates
interaction with the application’s interface (forms,
menus, buttons, etc.). small programs and attaches them to events associ-
ated with objects, as shown in Figure 13.1. In this
For example, rather than having a main procedure
way, the behavior of the application is determined by
that executes an order entry module followed by a the interaction of a number of small manageable pro-
data verification module followed by an inventory
grams rather than one large program.
update module, an event-driven application remains
in the background until certain events happen: when
a value in a field is modified, a small data verification
program is executed; when the user indicates that


13. Event-Driven Programming Using Macros Introduction: What is event-driven programming?

13.1.1 Triggers
FIGURE 13.1: In a trigger, a procedure is
attached to an event. Since events on forms “trigger” actions, event/proce-
dure combinations are sometimes called triggers.
An object, such as the
interface object button created in For example, the action query you attached to a but-
cmdUpdateCredits Section 11.3.5, has ton in Section 11.3.5 is an example of a simple, one-
predefined properties and action trigger. However, since an action query can
properties events. For a button, the
Caption most important event is only perform one type of action, and since you typi-
Enabled On Click. cally have a number of actions that need to be per-
... formed, macros or Visual Basic procedures are
events procedure typically used to implement a triggers in Access.
On Click
On Got Focus
... 13.1.2 The Access macro language
As you discovered in Tutorial 12, writing simple VBA
A procedure (such as an programs is not difficult, but it is tedious and error-
action query, macro, or VBA prone. Furthermore, as you will see in Tutorial 14,
function or subroutine) can be VBA programming becomes much more difficult
attached to an event. When
the event occurs, the when you have to refer to objects using the naming
procedure is executed. conventions of the database object hierarchy. As a
consequence, even experienced Access program-


13. Event-Driven Programming Using Macros Learning objectives

mers often turn to the Access macro language to attach the procedure to the correct event of the cor-
implement basic triggers. rect object.
The macro language itself consists of 40 or so com-
Selecting the correct object and the correct
mands. Although it is essentially a procedural lan-
event for a trigger is often the most difficult
guage (like VBA), the commands are relatively high
part of creating an event-driven application. It
level and easy to understand. In addition, the macro
is best to think about this carefully before you
editor simplifies the specification of the action argu-
get too caught up in implementing the proce-
ments (parameters).
dure.
13.1.3 The trigger design cycle

To create a trigger, you need to answer two ques-
tions: What is event-driven programming? What is a
trigger?
1. What has to happen?
2. When should it happen? How do I design a trigger?
Once you have answered the first question (“what”), How does the macro editor in Access work?
you can create a macro (or VBA procedure) to exe- How do I attach a macro to an event?
cute the necessary steps. Once you know the
answer to the second question (“when”), you can
What is the SetValue action? How is it used?


13. Event-Driven Programming Using Macros Tutorial exercises

How do I make the execution of particular 13.3.1 The basics of the macro editor
macro actions conditional? In this section, you are going to eliminate the warn-
What is a switchboard and how do I create ing messages that precede the trigger you created
one for my application? Section 11.3.5.
How to I make things happen when the As such, the answer to the “what” question is the fol-
application is opened? lowing:
What are the advantages and disadvantages 1. Turn off the warnings so the dialog boxes do not
of event-driven programming? pop up when the action query is executed;
2. Run the action query; and,
13.3 Tutorial exercises 3. Turn the warnings back on (it is generally good
programming practice to return the environment
In this tutorial, you will build a number of very simple
to its original state).
triggers using Access macros. These triggers, by
themselves, are not particularly useful and are Since a number of things have to happen, you can-
intended for illustrative purposes only. not rely on an action query by itself. You can, how-
ever, execute a macro that executes several actions
including one or more action queries.



• Select the Macros tab from the database window
FIGURE 13.4: Bring up the On Click property for
and press New. This brings up the macro editor
the button.
• Add the three commands as shown in
Figure 13.3. Note that the OpenQuery command
is used to run the action query.
• Save the macro as mcrUpdateCredits and
close it.

13.3.2 Attaching the macro to the event
The answer to the “when” question is: When the
cmdUpdateCredits button is pressed. Since you
already created the button in Section 11.3.5, all you
need to do is modify its On Click property to point the
mcrUpdateCredits macro.
• Open frmDepartments in design mode.
• Bring up the property sheet for the button and
scroll down until you find the On Click property,
The button wizard attached a
as shown in Figure 13.4. VBA procedure to the button.



FIGURE 13.2: The macro editor.

Macro actions can be selected from a list. The
SetWarnings command is used to turn the warning In the comment column, you can
messages (e.g., before you run an action query) on and off. document your macros as required

Multiple commands are
executed from top to
bottom.

Most actions have one or
more arguments that
determine the specific
behavior of the action. In
this case, the
SetWarnings action is
set to turn warnings off.

The area on the right
displays information about
the action.



FIGURE 13.3: Create a macro that answers the “what” question.

the macro. commands to
Add the three

SetWarningsfor the two
The arguments
actions
are straightforward. For the
OpenQuery command,
you can select the query to
open (or run) from a list.
Since this is an action
query, the second and third
arguments are not
applicable.



• Press the builder button ( ) beside the existing
FIGURE 13.5: Select the macro to attach to the
procedure and look at the VBA subroutine cre-
On Click property.
ated by the button wizard. Most of this code is for
error handling.

Unlike the stand-along VBA modules you cre-
ated in Tutorial 12, this module (collection of

of available macrosget a list
functions and subroutines) is embedded in Press the arrow to
the frmDepartments form.

• Since you are going to replace this code with a
macro, you do not want it taking up space in your
database file. Highlight the text in the subroutine
and delete it. When you close the module win-
dow, you will see the reference to the “event pro-
cedure” is gone.
• Bring up the list of choice for the On Click prop-
erty as shown in Figure 13.5. Select mcrUp-
dateCredits.



• Switch to form view and press the button. Since to modify the structure of the table until the
no warnings appear, you may want to press the query or form is closed.
button a few times (you can always use your roll-
back query to reset the credits to their original • Set the Caption property to Credits updated?
values). and the Default property to No as shown in
Figure 13.6.
13.3.3 Creating a check box to display Changes made to a table do not automatically carry
update status information over to forms already based on that table. As such,
Since the warning boxes have been disabled for the you must manually add the new field to the depart-
update credits trigger, it may be useful to keep track ments form.
of whether courses in a particular department have • Open frmDepartments in design mode.
already been updated. • Make sure the toolbox and field list are visible.
Notice that the new field (CrUpdated) shows up
To do this, you can add a field to the Departments
in the field list.
table to store this “update status” information.
• Use the same technique for creating combo
• Edit the Departments table and add a Yes/No
boxes to create a bound check box control for the
field called CrUpdated.
yes/no field. This is shown in Figure 13.7.
If you have an open query or form based on
the Departments table, you will not be able



this section, you are going to use one of the most
FIGURE 13.6: Add a field to the Departments
useful commands—SetValue—to automatically
table to record the status of updates.
change the value of the CrUpdated check box.
• Open your mcrUpdateCredits macro in design
mode and add a SetValue command to change
the CrUpdated check box to Yes (or True, if
you prefer). This is shown in Figure 13.8.
• Save the macro and press the button on the form.
Notice that the value of the check box changes,
reminding you not to update the courses for a
particular department more than once.

13.3.5 Creating conditional macros
Rather than relying on the user not to run the update
when the check box is checked, you may use a con-
ditional macro to prevent an update when the
check box is checked.
13.3.4 The SetValue command
So far, you have used two commands in the Access
macro language: SetWarnings and OpenQuery. In



FIGURE 13.7: Add a check box control to keep track of the update status.

from the toolbox.box tool
Select the check

A check box is a control
that can be bound to fields
of the yes/no data type.
When the box is checked,
True is stored in the
table; when the box is
field list to the detail section.from the
Drag the CrUpdated field unchecked, False is
stored.



FIGURE 13.8: Add a SetValue command to set the value of the update status field when the
update is compete.

from the SetValue command
Pick
the list or simply type it in.

The Item argument is the thing you The Expression argument is the
value you want the SetValue
want the SetValue action to set the action to set the value of the Item
value of. You can use the builder or to. Type in Yes (no quotation
simply type in CrUpdate. marks are required since Yes is
recognized as a constant in this
context).



• Select View Conditions to display the condi- 13.3.5.1 The simplest conditional macro
tions column in the macro editor as shown in If there is an expression in the condition column of a
Figure 13.9. macro, the action in that row will execute if the condi-
FIGURE 13.9: Display the macro editors tion is true. If the condition is not true, the action will
condition column be skipped.
• Fill in the condition column as shown in
Figure 13.10. Precede the actions you want to
execute if the check box is checked with [CrUp-
dated]. Precede the actions you do not want to
execute with Not [CrUpdated].

Since CrUpdated is a Boolean (yes/no) vari-
able, you do not need to write [CrUpdated]
= True or [CrUpdated] = False. The

“conditions” Conditions toolpress the
Select View or true and false parts are implied. However, if a
button on the bar. non-Boolean data type is used in the expres-
sion, a comparison operator must be included
(e.g., [DeptCode] = “COMM”, [Cred-
its] 3, etc.)



FIGURE 13.10: Create a conditional macro to control which actions execute.

is true if the CrUpdated check box is
The expression Not [CrUpdated]

not checked. Use this expression in
front of the actions you want to execute
in this situation.

true if the CrUpdated check box is
The expression [CrUpdated] is

checked. In this situation, you should
indicate to the user that the update is
not being performed.

The MsgBox action displays a
standard Windows message box. You
can set the message and other message
box features in the arguments section.



• Switch to the form and test the macro by pressing 13.3.5.2 Refining the conditions
the button. If the CrUpdated check box is The macro shown in Figure 13.10 can be improved
checked, you should get a message similar to by using an ellipsis (…) instead of repeating the
that shown in Figure 13.11. same condition in line after line. In this section, you
FIGURE 13.11: The action query is not executed will simplify your conditional macro slightly.
and the message box appears instead. Move the message box action and condition to the
top of the list of actions by dragging its record selec-
tor (grey box on the left).
• Insert a new row immediately following the mes-
sage and add a StopMacro action, as shown in
Figure 13.12.
The macro in Figure 13.12 executes as follows: If
CrUpdate is true (i.e., the box is checked), the
MsgBox action executes. Since the next line has an
ellipsis in the condition column, the condition contin-
ues to apply. However, that action on the ellipsis line
is StopMacro, and thus the macro ends without
executing the next four lines.



If the CrUpdate box is not checked, the first two
FIGURE 13.12: Rearrange the macro actions and
lines are ignored (i.e., the lines with the false condi-
insert a new row.
tion and the ellipsis) and the update proceeds.

message box action to theand drag thelist.
Click the record selector
top of the
13.3.5.3 Creating a group of named macros
It is possible to store a number of related macros

Add an ellipsis together in one macro “module”. These group mac-
(…) and a ros have two advantages:
StopMacro
action. 1. Modular macros can be created — instead of
having a large macro with many conditions and
branches, you can create a small macro that call
other small macros.
2. Similar macros can be grouped together — for
example, you could keep all you Departments-
related macros or search-related macros in a
macro group.

to insert a new rowyou would like
Right-click where
and select
In this section, we will focus on the first advantage.
• Select View Macro Names to display the macro
Insert Row from the popup menu.
name column.



• Perform the steps in Figure 13.13 to modularize • Remove the scroll bars, navigation buttons, and
your macro. record selectors from the form using the form’s
• Change the macro referred to in the On Click property sheet.
property of the cmdUpdateCredits button from • Save the form as swbMain.
mcrUpdateCredits to There are two ways to add button-based triggers to a
mcrUpdateCredits.CheckStatus. form:
• Test the operation of the button.
1. Turn the button wizard off, create the button, and
attach an macro containing the appropriate
13.3.6 Creating switchboards
action (or actions).
One of the simplest (but most useful) triggers is an 2. Turn the button wizard on and use the wizard to
OpenForm command attached to a button on a form select from a list of common actions (the wizard
consisting exclusively of buttons. writes a VBA procedure for you).
This type of “switchboard” (as shown in
Figure 13.14) can provide the user with a means of Since the wizard can only attach one action to
navigating the application. a button (such as opening a form or running
• Create an unbound form as shown in an action query) it is less flexible than a
Figure 13.15. macro. However, once you are more comfort-
able with VBA, there is nothing to stop you



FIGURE 13.13: Use named macros to modularize the macro.

the macro names column. to display
Select View Macro Names A macro executes until it encounters a
blank line. Use blank lines to separate the
named macros within a group.

CheckStatusmacro called the
Create a named
that contains
conditional logic for the procedure.

Create two other macros, Updated and
NotUpdated that correspond to the
logic in the CheckStatus macro.

particular macro. action executes a to
The RunMacro
Select the macro
execute from a list in the arguments pane.
Note the naming convention for macros
within a macro group.



FIGURE 13.14: A switchboard interface to the application.

The command buttons are placed on an Although it is not shown here, switchboards can
unbound form. Note the absence of scroll bars, call other switchboards, allowing you to add a
record selectors, or navigation buttons. hierarchical structure to your application.

Gratuitous clip art can be used to Shortcut keys are include on each
clutter your forms and reduce the button to allow the user to navigate
application’s overall performance. the application with keystrokes.



FIGURE 13.15: Create an unbound form as the
switchboard background.

leave the “record source”wizard) and
Select Design View (no
box empty.

you can buildayour switchboard.
The result is blank form on which



from editing the VBA modules created by the • Follow the directions provided by the wizard to
wizard to add additional functionality. set the action for the button (i.e., open the frm-
Courses form) as shown in Figure 13.17.
13.3.6.1 Using a macro and manually-created • Change the button’s font and resize it as
buttons required.
• Ensure the wizard is turned off and use the but-
ton tool to create a button. You can standardize the size of your form
• Modify the properties of the button as shown in objects by selecting more than one and using
Figure 13.16. Format Size to Tallest and to Widest com-
• Create a macro called mands. Similarly, you can select more than
mcrSwitchboard.OpenDept and use the one object and use the “multiple selection”
OpenForm command to open the form frmDe- property sheet to set the properties all at
partments. once.
• Attach the macro to the On Click event of the
cmdDepartments button. 13.3.7 Using an autoexec macro
• Test the button. If you use the name autoexec to save a macro (in
13.3.6.2 Using the button wizard lieu of the normal mcrname convention), Access
• Turn the button wizard back on and create a new will execute the macro actions when the database is
button. opened. Consequently, auto-execute macros are



FIGURE 13.16: Create a button and modify its appearance.

(ensure the wizard activated).a button
Use the button tool to create
(e.g., cmdDepartments) and caption
Give the button a meaningful name
(including a shortcut key.).

Scroll down the property sheet and change
the value of the button’s Font Size property.
Resize the button by dragging its handles.



FIGURE 13.17: Use the command button wizard to create a button for the switchboard.

the action type associated with the button.as
Select Form Operations Open Form

Provide a caption
for the button.

from the list. form
Select the correct



often used to display a switchboard when the user from the menu system. Consequently, you need to
starts the application. know something about the menu structure of Access
Another typical auto-execute operation is to hide the before you create your macro.
database window. By doing this, you unclutter the
screen and reduce the risk of a user accidentally
making a change to the application (by deleting a
In version 8.0, the DoMenuItem action has
been replaced by the slightly more intuitive
RunCommand action. See on-line help for
database object, etc.).
more information on RunCommand.
To unhide the database window, select Win-
• Create an auto-execute macro
dow Unhide from the main menu or press
• Add the DoMenuItem and OpenForm actions to
the database window icon ( ) on the toolbar.
hide the database window and open the main
The problem with hiding the database window using switchboard, as shown in Figure 13.18.
a macro is that there is no HideDatabaseWindow • Close the database and reopen it after a short
command in the Access macro language. As such, delay to test the macro.
you have to rely on the rather convoluted DoMenu-
In version 7.0 and above, you do not need to
Item action.
use an autoexec macro to hide the database
As its name suggests, the DoMenuItem action per- window and open a form. Instead, you can
forms an operation just as if it had been selected right-click on the database window, select


13. Event-Driven Programming Using Macros Discussion

13.4 Discussion
FIGURE 13.18: Create an auto-execute macro.
13.4.1 Event-driven programming versus
conventional programming
The primary advantages of event-driven program-
ming are the following:
1. Flexibility — since the flow of the application is
controlled by events rather than a sequential pro-
gram, the user does not have to conform to the
programmer’s understanding of how tasks should
be executed.
WindowDoMenuItem action, select the
For the
Hide commands from the
2. Robustness — Event-driven applications tend to
be more robust since they are less sensitive to
Database menu (i.e., the menu that is active
when the database window is being used). the order in which users perform activities. In
conventional programming, the programmer has
to anticipate virtually every sequence of activities
Startup, and fill in the properties for the appli- the user might perform and define responses to
cation. these sequences.


13. Event-Driven Programming Using Macros Application to the assignment

The primary disadvantage of event-driven programs • Create a main switchboard for you application. It
is that it is often difficult to find the source of errors should provide links to all the database objects
when they do occur. This problem arises from the your user is expected to have access to (i.e., your
object-oriented nature of event-driven applications— forms).
since events are associated with a particular object
you may have to examine a large number of objects
before you discover the misbehaving procedure.
This is especially true when events cascade (i.e., an
event for one object triggers an event for a different
object, and so on).

• Add “update status” check boxes to you transac-
tion processing forms (i.e., Orders and Ship-
ments)
• Create a conditional macro for your Shipments
form to prevent a particular shipment from being
added to inventory more than once.


Access Tutorial 14: Data Access Objects
14.1 Introduction: What is the DAO that its modularity supports easier development and
hierarchy? maintenance of applications.
The disadvantage is that is you have to understand a
The core of Microsoft Access and an important part
large part of the hierarchy before you can write your
of Visual Basic (the stand-alone application develop-
ment environment) is the Microsoft Jet database first line of useful code. This makes using VBA diffi-
cult for beginners (even for those with considerable
engine. The relational DBMS functionality of Access
comes from the Jet engine; Access itself merely pro- experience writing programs in BASIC or other
3GLs*).
vides a convenient interface to the database engine.
Because the application environment and the data- 14.1.1 DAO basics
base engine are implemented as separate compo-
Although you probably do not know it, you already
nents, it is possible to upgrade or improve Jet
have some familiarity with the DAO hierarchy. For
without altering the interface aspects of Access, and
example, you know that a Database object (such as
vice-versa.
univ0_vx.mdb) contains other objects such as
Microsoft takes this component-based approach fur- tables (TableDef objects) and queries (QueryDef
ther in that the interface to the Jet engine consists of objects). Moving down the hierarchy, you know that
a hierarchy of components (or “objects”) called Data TableDef objects contain Field objects.
Access Objects (DAO). The advantage of DAO is
* Third-generation programming languages.


14. Data Access Objects Introduction: What is the DAO hierarchy?

Unfortunately, the DAO hierarchy is somewhat more every object has a number of properties that can be
complex than this. However, at this level, it is suffi- either observed (read-only properties) or set (read/
cient to recognize three things about DAO: write properties). For example, each TableDef (table
1. Each object that you create is an instance of a definition) object has a read-only property called
class of similar objects (e.g., univ0_vx is a par- DateCreated and a read/write property called Name.
ticular instance of the class of Database objects). To access an object’s properties in VBA, you nor-
2. Each object may contain one or more Collec- mally use the object name.property
tions of objects. Collections simply keep all name syntax, e.g.,
objects of a similar type or function under one Employees.DateCreated.
umbrella. For example, Field objects such as
To avoid confusion between a property called
DeptCode and CrsNum are accessible through a
DateCreated and a field (defined by you)
Collection called Fields).
called DateCreated, Access version 7.0
3. Objects have properties and methods (see
and above require that you use a bang (!)
below).
instead of a period to indicate a field name or
some other object created by you as a devel-
14.1.2 Properties and methods
oper. For example:
You should already be familiar with the concept of Employees!DateCreated.Value
object properties from the tutorial on form design identifies the Value property of the DateCre-
(Tutorial 6). The idea is much the same in DAO:



ated field (assuming one exists) in the object summaries in the on-line help if you are
Employees table. unsure.

Methods are actions or behaviors that can be A more obvious example of a method is the Cre-
applied to objects of a particular class. In a sense, ateField method of TableDef objects, e.g.:
they are like predefined functions that only work in Employees.CreateField(“Phone”,
the context of one type of object. For example, all dbText, 25)
Field objects have a method called FieldSize that This creates a field called Phone, of type dbText (a
returns the size of the field. To invoke a object’s constant used to represent text), with a length of 25
methods, you use the characters.
object name.method [parameter1,
..., parametern] syntax, e.g.,: 14.1.3 Engines, workspaces, etc.
DeptCode.FieldSize. A confusing aspect of the DAO hierarchy is that you
cannot simply refer to objects and their properties as
A reasonable question at this point might be:
done in the examples above. As Figure 14.1 illus-
Isn’t FieldSize a property of a field, not a
trates, you must include the entire path through the
method? The answer to this is that the imple-
hierarchy in order to avoid any ambiguity between,
mentation of DAO is somewhat inconsistent in
say, the DeptCode field in the Courses TableDef
this respect. The best policy is to look at the
object and the DeptCode field in the qryCourses
QueryDef object.



FIGURE 14.1: Navigating the DAO hierarchy.

To access a particular field, you DBEngine By creating a database object at
have to understand the structure the start of your VBA
of the DAO hierarchy. programs, you bypass the top
Workspaces part of the hierarchy.

Databases other classes...

TableDefs QueryDefs Recordsets other classes...

Courses other tables... qryCourses other queries...

Fields Fields
Legend
DeptCode DeptCode
TableDefs object or collection
Indexes Indexes
Courses instance


14. Data Access Objects Learning objectives

Working down through the hierarchy is especially 14.3 Tutorial exercises
confusing since the first two levels (DBEngine and
Workspaces) are essentially abstractions that have 14.3.1 Setting up a database object
no physical manifestations in the Access environ-
In this section you will write VBA code that creates a
ment. The easiest way around this is to create a pointer to the currently open database.
Database object that refers to the currently open
• Create a new module called basDAOTest (see
database (e.g., univ0_vx.mdb) and start from the Section 12.3.3 for information on creating a new
database level when working down the hierarchy.
module).
Section 14.3.1 illustrates this process for version 2.0.
• Create a new subroutine called PrintRecords.
• Define the subroutine as follows:
14.2 Learning objectives Dim dbCurr As DATABASE
What is the DAO hierarchy? Set dbCurr =
What are objects? What are properties and DBEngine.Workspaces(0).Databases(0)
methods? Debug.Print dbCurr.Name

How do I create a reference to the current
• Run the procedure, as shown in Figure 14.2.
Let us examine these three statements one by one.
database object? Why is this important?
What is a recordset object?
1. Dim dbCurr As DATABASE
This statement declares the variable dbCurr as
How do I search a recordset? an object of type Database. For complex objects


14. Data Access Objects Tutorial exercises

FIGURE 14.2: Create a pointer to the current database.

(dbCurr) toset the pointer
Declare and
the current
database.

of thea database. the name
Add line to print

Although you can use the
Print statement by itself
Run the procedure to
ensure it works.
in the debug window, you
must invoke the Print
method of the Debug object Version 7.0 and above support a less
from a module—hence the cumbersome way referring to the current
Debug.Print syntax. database—the CurrentDb function:
Set dbCurr = CurrentDb



(in contrast to simple data types like integer, Do not worry if you are not completely sure
string, etc.) Access does not allocate memory what is going on at this point. As long as you
space for a whole database object. Instead, it understand that you can type the above two
allocates space for a pointer to a database lines to create a pointer to your database,
object. Once the pointer is created, you must set then you are in good shape.
it to point to an object of the declared type (the
object may exist already or you may have to cre- 3. Debug.Print dbCurr.Name
ate it). This statement prints the name of the object to
2. Set dbCurr = DBEngine.Work- which dbCurr refers.
spaces(0).Databases(0)
(Note: this should be typed on one line). In this 14.3.2 Creating a Recordset object
statement, the variable dbCurr (a pointer to a As its name implies, a TableDef object does not con-
Database object) is set to point to the first Data- tain any data; instead, it merely defines the structure
base in the first Workspace of the only Database of a table. When you view a table in design mode,
Engine. Since the numbering of objects within a you are seeing the elements of the TableDef object.
collection starts at zero, Databases(0) indi- When you view a table in datasheet mode, in con-
cates the first Database object. Note that the first trast, you are seeing the contents of Recordset
Database object in the Databases collection is object associated with the table.
always the currently open one.



To access the data in a table using VBA, you have to 2. Sets rsCourses to point to the newly created
invoke the OpenRecordset method of the Data- recordset.
base object. Since most of the processing you do in Note that this Set statement is different than the pre-
VBA involves data access, familiarity with Recordset vious one since the OpenRecordset method
objects is essential. In this section, you will create a results in a new object being created (dbCurr points
Recordset object based on the Courses table. to an existing database—the one you opened when
• Delete the Debug.Print dbCurr.Name line you started Access).
from your program.
• Add the following: 14.3.3 Using a Recordset object
Dim rsCourses As Recordset In this section, you will use some of the properties
Set rsCourses = and methods of a Recordset object to print its con-
dbCurr.OpenRecordset(“Courses”)
tents.
The first line declares a pointer (rsCourses) to a • Add the following to PrintRecords:
Recordset object. The second line does two things:
Do Until rsCourses.EOF
1. Invokes the OpenRecordset method of dbCurr Debug.Print rsCourses!DeptCode “ ”
to create a Recordset object based on the table rsCourses!CrsNum
named “Courses”. (i.e., the name of the table is rsCourses.MoveNext
a parameter for the OpenRecordset method). Loop
• This code is explained in Figure 14.3.



FIGURE 14.3: Create a program to loop through the records in a Recordset object.

EOF is a property of the recordset.
It is true if the record counter has
reached the “end of file” (EOF)
marker and false otherwise.

The exclamation mark (!) indicates
that DeptCode is a user-defined
field (rather than a method or
property) of the recordset object.

Since the Value property is the default property
of a field, you do not have to use the
recordset!field.Value syntax.

The MoveNext method moves the
record counter to the next record in
the recordset.



14.3.4 Using the FindFirst method WHERE condition (a string) that ensures that only one
In this section, you will use the FindFirst method record is found.
of Recordset objects to lookup a specific value in a For example, to get the Title of COMM 351 from
table. the Courses table, you would provide MyLookUp()
• Create a new function called MyLookUp() using with the following parameters:
the following declaration: 1. “Title” — a string containing the name of the
Function MyLookUp(strField As field from which we want to return a value;
String, strTable As String, 2. “Course” — a string containing the name of the
strWhere As String) As String source table; and,
An example of how you would use this function is to 3. “DeptCode = ‘COMM’ AND CrsNum =
return the Title of a course from the Courses ‘335’” — a string that contains the entire
table with a particular DeptCode and CrsNum. In WHERE clause for the search.
other words, MyLookUp() is essentially an SQL
statement without the SELECT, FROM and WHERE Note that both single and double quotation
clauses. marks must be used to signify a string within a
The parameters of the function are used to specify string. The use of quotation marks in this
the name of the table (a string), the name of the field manner is consistent with standard practice in
(a string) from which you want the value, and a English. For example, the sentence:
“He shouted, ‘Wait for me.’” illus-



trates the use of single quotes within double Recordset object to be opened (the Find-
quotes. First method only works with “dynaset” type
recordsets, hence the need to include the
• Define the MyLookUp() function as follows: additional parameter in this segment of code).
Dim dbCurr As DATABASE
Set dbCurr = CurrentDb rsRecords.FindFirst strWhere

If you are using version 2.0, you cannot use VBA uses a rather unique convention to
the CurrentDb method to return a pointer to determine whether to enclose the arguments
the current database. You must use long form of a function, subroutine, or method in paren-
(i.e., Set dbCurr = DBEngine…) theses: if the procedure returns a value,
enclose the parameters in parentheses; oth-
Dim rsRecords As Recordset erwise, use no parentheses. For example, in
Set rsRecords = the line above, strWhere is a parameter of
dbCurr.OpenRecordset(strTable, the FindFirst method (which does not
dbOpenDynaset)
return a value).

In version 2.0, the name of some of the pre-
defined constants are different. As such, you
If Not rsRecords.NoMatch() Then
MyLookUp =
must use DB_OPEN_DYNASET rather than
rsRecords.Fields(strField).Value
dbOpenDynaset to specify the type of



Else need in your application, it is occasionally necessary
MyLookUp = “” to perform a stand-alone query—that is, to use the
End If DLookUp() function to retrieve a value from a table
• Execute the function with the following statement or query.
(see Figure 14.4): When using DLookUp() for the first few times, the
? MyLookUp(“Title”, “Courses”, syntax of the function calls may seem intimidating.
“DeptCode = 'COMM' AND CrsNum = But all you have to remember is the meaning of a
'351'”)
handful of constructs that you have already used.
As it turns out, what you have implemented exists These constructs are summarized below:
already in Access in the form of a predefined func- • Functions — DLookUp() is a function that
tion called DLookUp(). returns a value. It can be used in the exact same
• Execute the DLookUp() function by calling it in manner as other functions, e.g.,
the same manner in which you called x = DLookUp(…) is similar to
MyLookUp(). x = cos(2*pi).
• Round brackets ( ) — In Access, round brackets
14.3.5 The DLookUp() function have their usual meaning when grouping
The DLookUp() function is the “tool of last resort” in together operations, e.g., 3*(5+1). Round
Access. Although you normally use queries and brackets are also used to enclose the arguments
recordsets to provide you with the information you of function calls, e.g., x = cos(2*pi).



FIGURE 14.4: MyLookUp(): A function to find a value in a table.

The NoMatch() method returns True if the
FindFirst method finds no matching records,
and False otherwise.

Since strField contains the name of a valid
Field object (Title) in the Fields collection,
this notation returns the value of Title.



• Square brackets [ ] — Square brackets are not x = COMM means that the variable x is equal to
a universally defined programming construct like the value of the variable COMM.
round brackets. As such, square brackets have a • Single quotation marks ‘ ’ — Single quotation
particular meaning in Access/VBA and this marks have only one purpose: to replace normal
meaning is specific to Microsoft products. Simply quotation marks when two sets of quotation
put, square brackets are used to signify the name marks are nested. For example, the expression
of a field, table, or other object in the DAO hierar- x = “[ProductID] = ‘123’” means that the
chy—they have no other meaning. Square brack- variable x is equal to the string ProductID =
ets are mandatory when the object names “123”. In other words, when the expression is
contain spaces, but optional otherwise. For evaluated, the single quotes are replaced with
example, [Forms]![frmCourses]![Dept- double quotes. If you attempt to nest two sets of
Code] is identical to Forms!frm- double quotation marks (e.g., x = “[Produc-
Courses!DeptCode. tID] = “123””) the meaning is ambiguous
• Quotation marks “ ” — Double quotation marks and Access returns an error.
are used to distinguish literal strings from names • The Ampersand — The ampersand is the con-
of variables, fields, etc. For example, catenation operator in Access/VBA and is unique
x = “COMM” means that the variable x is equal to Microsoft products. The concatenation opera-
to the string of characters COMM. In contrast, tor joins two strings of text together into one
string of text. For example,



x = “one” “_two” means that the variable • Create a calculated field called Title using the
x is equal to the string one_two. following expression (see Figure 14.5):
If you understand these constructs at this point, then Title: DLookUp(“Title”, “Courses”,
understanding the DLookUp() function is just a mat- “DeptCode = ‘” [DeptCode] “’ AND
ter of putting the pieces together one by one. CrsNum = ‘” [CrsNum] “’”)
14.3.5.2 Understanding the WHERE clause
14.3.5.1 Using DLookUp() in queries
The first two parameters of the DLookUp() are
The DLookUp() function is extremely useful for per-
straightforward: they give the name of the field and
forming lookups when no relationship exists between
the table containing the information of interest. How-
the tables of interest. In this section, you are going to
ever, the third argument (i.e., the WHERE clause) is
use the DLookUp() function to lookup the course
more complex and requires closer examination.
name associated with each section in the Sections
table. Although this can be done much easier using a At its core, this WHERE clause is similar to the one
join query, this exercise illustrates the use of vari- you created in Section 5.3.2 in that it contains two
ables in function calls. criteria. However, there are two important differ-
• Create a new query called qryLookUpTest ences:
based on the Sections table. 1. Since it is a DLookUp() parameter, the entire
• Project the DeptCode, CrsNum, and Section clause must be enclosed within quotation marks.
fields. This means single and double quotes-within-
quotes must be used.



FIGURE 14.5: Create a query that uses DLookUp().

table onlyquerynot includethe Sections
Create a
(do
based on
Courses). correct course title for function to get the
Use the DLookUp()
each section.


14. Data Access Objects Discussion

2. It contains variable (as opposed to literal) criteria. • Use strWhere in a DLookUp() call.
For example, [DeptCode] is used instead of
“COMM”. This makes the value returned by the 14.4 Discussion
function call dependent on the current value of
the DeptCode field. 14.4.1 VBA versus SQL
In order to get a better feel for syntax of the function The PrintRecords procedure you created in
call, do the following exercises (see Figure 14.6): Section 14.3.3 is interesting since it does essentially
Switch to the debug window and define two string the same thing as a select query: it displays a set of
variables (see Section 12.3.1 for more information records.
on using the debug window): You could extend the functionality of the Print-
strDeptCode = “COMM” Records subroutine by adding an argument and an
strCrsNum = “351” IF-THEN condition. For example:
These two variables will take the place the field val- Sub PrintRecords(strDeptCode as
ues while you are in the debug window. String)
• Write the WHERE clause you require without the Do Until rsCourses.EOF
variables first. This provides you with a template If rsCourses!DeptCode = strDeptCode
Then
for inserting the variables.
• Assign the WHERE clause to a string variable Debug.Print rsCourses!DeptCode “ ”
rsCourses!CrsNum
called strWhere (this makes it easier to test).



FIGURE 14.6: Examine the syntax of the WHERE clause.

values of DeptCode and CrsNum.valid
Create string variables that refer to
criteriathe WHERE clause using literal
Write
first to get a sense of what is
required.

Use the variables in the WHERE
clause and assign the expression to a
string variable called strWhere.

third parameter of the DLookUp()the
To save typing, use strWhere as

call.

When replacing a literal string with a variable, you
have to stop the quotation marks, insert the variable
(with ampersands on either side) and restart the
quotation marks. This procedure is evident when the
literal and variable version are compared to each other.



End If SQL and QBE are declarative languages because
rsCourses.MoveNext you (as a programmer) need only tell the computer
Loop what you want done, not how to do it. In contrast,
rsCourses.Close VBA is a procedural language since you must tell the
End Sub computer exactly how to extract the records of inter-
This subroutine takes a value for DeptCode as an est.
argument and only prints the courses in that particu- Although procedural languages are, in general, more
lar department. It is equivalent to the following SQL flexible than their declarative counterparts, they rely
command: a great deal on knowledge of the underlying struc-
SELECT DeptCode, CourseNum FROM ture of the data. As a result, procedural languages
Courses WHERE DeptCode = tend to be inappropriate for end-user development
strDeptCode (hence the ubiquity of declarative languages such as
SQL in business environments).
14.4.2 Procedural versus Declarative
The difference between extracting records with a
query language and extracting records with a pro-
gramming language is that the former approach is
declarative while the latter is procedural.


14. Data Access Objects Application to the assignment

14.5 Application to the assignment As a result, it is possible to cheat a little bit and cre-
ate a stand-alone table (e.g., SystemVariables)
14.5.1 Using a separate table to store that contains a single record:
system parameters VariableName Value
When you calculated the tax for the order in GST 0.07
Section 9.5, you “hard-coded” the tax rate into the
form. If the tax rate changes, you have to go through
Of course, other system-wide variables could be
all the forms that contain a tax calculation, find the
contained in this table, but one is enough for our pur-
hard-coded value, and change it. Obviously, a better
poses. The important thing about the SystemVari-
approach is to store the tax rate information in a
ables table is that it has absolutely no relationship
table and use the value from the table in all form-
with any other table. As such, you must use a
based calculations.
DLookUp() to access this information.
Strictly speaking, the tax rate for each product is a • Create a table that contains information about the
property of the product and should be stored in the tax rate.
Products table. However, in the wholesaling envi- • Replace the hard-coded tax rate information in
ronment used for the assignment, the assumption is your application with references to the value in
made that all products are taxed at the same rate. the table (i.e., use a DLookUp() in your tax cal-
culations). Although the SystemVariables
table only contains one record at this point, you



should use an appropriate WHERE clause to The reason you must use a DLookUp() to get this
ensure that the value for GST is returned (if no information is that there is no relationship between
WHERE clause is provided, DLookUp() returns the OrderDetails and BackOrders tables.
the first value in the table).
Any relationship that you manage to create
The use of a table such as SystemVari- between OrderDetails and BackOrders
ables contradicts the principles of relational will be nonsensical and result in a non-updat-
database design (we are creating an attribute able recordset.
without an entity). However, trade-offs
between theoretical elegance and practicality • In the query underlying your OrderDetails
are common in any development project. subform, create a calculated field called QtyOn-
BackOrder to determine the number of items on
14.5.2 Determining outstanding backorder for each item added to the order. This
backorders calculated field will use the DLookUp() function.
An good example in your assignment of a situation There are two differences between this DLookUp()
requiring use of the DLookUp() is determining the and the one you did in Section 14.3.5.1
backordered quantity of a particular item for a partic- 1. Both of the variables used in the function (e.g.,
ular customer. You need this quantity in order to cal- CustID and ProductID) are not in the query.
culate the number of each item to ship. As such, you will have to use a join to bring the



missing information into the query. zero. To do this, use the iif() and IsNull()
2. ProductID is a text field and the criteria of text functions, e.g.:
fields must be enclosed in quotation marks, e.g.: QtyOnBackOrderNoNull:
ProductID = “123” iif(IsNull([QtyOnBackOrder]),0,[Qty
However, CustID is a numeric field and the crite- OnBackOrder])
ria for numeric fields is not enclosed in quotations • Use this “clean” version in your calculations and
marks, e.g.: on your form.
CustID = 4.
It is possible to combine these two calculated
Not every combination of CustID and Pro- fields into a one-step calculation, e.g.:
ductID will have an outstanding backorder. iif(IsNull(DLookUp(…)),0,
When a matching records is not found, the DLookUp(…)).
DLookUp() function returns a special value: The problem with this approach is that the
Null. The important thing to remember is DLookUp() function is called twice: once to
that Null plus or minus anything equals test the conditional part of the immediate if
Null. This has implications for your “quantity statement and a second time to provide the
to ship” calculation. “false” part of the statement. If the Back-
Orders table is very large, this can result in
• Create a second calculated field in your query to an unacceptable delay when displaying data
convert any Nulls in the first calculated field to in the form.


Access Tutorial 15: Advanced Triggers
15.1 Introduction: Pulling it all How do I create an unbound combo box?
together Can I implement the search capability using
In this tutorial, you will bring together several of the Visual Basic?
skills you have learned in previous tutorials to imple-
ment some sophisticated triggers. 15.3 Tutorial exercises

15.2 Learning objectives 15.3.1 Using a macro to run VBA code
How do I run VBA code using a macro?
There a some things that cannot be done using the
Access macro language. If the feature you wish to
How do I use the value in one field to implement is critical to your application, then you
automatically suggest a value for a different must implement it using VBA. However, since it is
field? possible to call a VBA function from within a macro,
How do I change the table or query a form is you do not have to abandon the macro language
bound to once the form is already created? completely.
What is the After Update event? How is it In this section, you are going to execute the Param-
used? eterTest subroutine you created in Section 12.3.6
How do I provide a search capability for my
from within a macro. Since the RunCode action of
the Access macro language can only be used to exe-
forms?


15. Advanced Triggers Tutorial exercises

cute functions (not subroutines) you must do one of 'this function calls the
two things before you create the macro: ParameterTest subroutine
ParameterTest intStart, intStop
1. Convert ParameterTest to a function — you do
this simply by changing the Sub at the start of the ParameterTestWrapper = True
'return a value
procedure to Function.
End Function
2. Create a new function that executes Parame-
• Call the function, as shown in Figure 15.1.
terTest and call the function from the macro.
15.3.1.1 Creating a wrapper Note that the return value of the function is
Since the second alternative is slightly more interest- declared as an integer, but the actual assign-
ment statement is ParameterTestWrap-
ing, it is the one we will use.
• Open your basTesting module from per = True. This is because in Access/
VBA, the constants True and False are
Tutorial 12.
• Create a new function called ParameterTest- defined as integers (-1 and 0 respectively).
Wrapper defined as follows:
15.3.1.2 Using the RunCode action
Function • Leave the module open (you may have to resize
ParameterTestWrapper(intStart As
and/or move the debug window) and create a
Integer, intStop As Integer) As
new macro called mcrRunCodeTest.
Integer



FIGURE 15.1: Create a function that calls the ParameterTest subroutine.

the ParameterTest
Create a function to call

subroutine.

Since ParameterTest invoke the function (do notto
Use the Print statement
forget
does not return a value, its the parameters).
arguments are not in
brackets.
The return value of
ParameterTestWrapper()
is True, so this is printed when
the function ends.



• Add the RunCode action and use the expression • Select Run Start to execute the macro as
builder to select the correct function to execute, shown in Figure 15.3.
15.3.2 Using activity information to
The expression builder includes two parame- determine the number of credits
ter place holders (intStart and
In this section, you will create triggers attached to the
intStop) in the function name. These
After Update event of bound controls.
are to remind you that you must pass two
parameters to the ParameterTestWrap- 15.3.2.1 Scenario
per() function. If you leave the place holders Assume that each type of course activity is generally
where they are, the macro will fail because associated with a specific number of credits, as
Access has not idea what intStart shown below:
and intStop refer to.
Activity Credits
• Replace the parameter place holders with two lecture 3.0
numeric parameters (e.g. 3 and 6). Note that in lab 3.0
general, the parameters could be field names or
tutorial 1.0
any other references to Access objects contain-
seminar 6.0
ing (in this case) integers.



FIGURE 15.2: Use the expression builder to select the function to execute.

action to the macro.
Add a RunCode

Note the intStart and
intStop parameter place
holders. These must be replaced
with expressions that Access
understands.

downthe expression builder to drill in
Use
to the user-defined functions
your database file.



Assume as well that the number of credits for a par-
FIGURE 15.3: Execute the RunCode macro.
ticular type of course is not cast in stone. As such,
the numbers given above are merely “default” val-
ues.
You want to use the default credit values when you
create a new course or modify an existing course.
However, the user may override this default if neces-
sary for a particular course. The basic requirement is
illustrated in Figure 15.4.
15.3.2.2 Designing the trigger
Based on the foregoing, the answer to the “what”

parameter place
Replace the question is the following:
1. Look up the default number of credits associated
holders.
with the course activity showing in the form’s
Activity field.
the toolRun toStart (or press the ! icon in
Select
bar) execute the macro.
2. Copy this number into the Courses.Credits
field.



FIGURE 15.4: Inserting a default value into a new record.

Create a new record for a lecture-based of creditsmacro to find the default number
Create a
and copy the value it into the
course: COMM 437: Database Technology Credits field.

Select “Lecture” from the list of list of
course activities created in Tutorial 8.

Since this is a new record, the default
value of Credits (like any numeric
field) is zero. You want to use the
information you just specified in the macrothe Activityvalue in the the
Once
executes. The
field is updated,
Activity field to automatically Credits field can be changed by the
look up the correct default number of user.
credits for a lecture course and insert
it in the Credits field.



There are several possible answers to the “when” • Ensure that you have a courses form (e.g., frm-
question (although some are better than others). For Courses) and that the form has a combo box for
example: the Activity field. You may wish to order the
1. When the user enters the Credits field (the On fields such that Activity precedes Credits in
Enter event for Credits) — The problem with the tab order (as shown in Figure 15.4).
this choice is that the user could modify the
If your move fields around, remember to
course’s activity without moving the focus to the
adjust the tab order accordingly (recall
Activity field. In such a case, the trigger would
Section 8.3.4).
not execute.
2. When the user changes the Activity field (the 15.3.2.4 Looking up the default value
After Update event for Activity) — This choice
As you discovered in Section 14.3.5, Access has a
guarantees that whenever the value of Activ-
DLookUp() function that allows you to go to the
ity is changed, the default value will be copied
Activities table and find the value of Credits
into the Credits field. As such, it is a better
for a particular value of Activity. A different
choice.
approach is to join the Activities table with the
15.3.2.3 Preliminary activities Courses table in a query so that the default value of
• Modify the Activities table to include a single- credits is always available in the form. This is the
precision numeric field called Credits. Add the approach we will use here.
values shown in the table in Section 15.3.2.1.



• Ensure you have a relationship (in the main rela-
FIGURE 15.5: Use a join to make the default
tionship window) between Courses.Activity
value available.
and Activities.Activity.
• Create a new query called qryCoursesAnd-
Credits based on the Courses and Activi-
ties tables (see Figure 15.5).

Notice that you have two credits fields:
Courses.Credits (the actual number of
credits for the course) and Activi-
ties.Credits (the “default” or “suggested”
number of credits based on the value of
Activity). Access uses the table
name.field name notation whenever a
query contains more than one field with the
same name.

Since you already have forms based on the
Courses table that expect a field called Credits
(rather than one called Courses.Credits), it is a



good idea to rename the Activities.Credits
FIGURE 15.6: Rename one of the Credits fields.
field in the query. You do this by creating a calculated
field.
• Rename Activities.Credits to Default-
Credits as shown in Figure 15.6. Note that this
eliminates the need for the table
name.field name notation.
15.3.2.5 Changing the Record Source of the
form
Rather than create a new form based on the qry-
CoursesAndCredits query, you can modify the
Record Source property of the existing frmCourses
form so it is bound to the query rather than the
Courses table.
• Bring up the property sheet for the frmCourses
form and change the Record Source property to
qryCoursesAndCredits as shown in
Figure 15.7.
table to DefaultCredits.Activities
Rename Credits form the



The advantage of using a join query in this manner is
FIGURE 15.7: Change the Record Source
that DefaultCredits is now available for use
property of an existing form.
within the form and within any macros or VBA mod-

changeup the form’sSource property.
Bring
its Record
property list and ules that run when the form is open.
15.3.2.6 Creating the SetValue macro
The SetValue macro you require here is extremely
simple once you have DefaultCredits available
within the scope of the form.
• Create the mcrCourses.SetCredits macro
15.3.2.7 Attaching a procedure to the After
Update event
The On Click event of a button is fairly simple to
understand: the event occurs when the button is
clicked. The events associated with non-button
objects operate in exactly the same way. For exam-
ple, the After Update event for controls (text box,
The field list now contains all
the fields in the new query. combo box, check box, etc.) occurs when the value



• Attach the mcrCourses.SetCredits macro to
FIGURE 15.8: Create the SetValue macro.
the After Update event of the Activity field.
• Verify that the trigger works properly.
and a named macro called SetCredits.
Create a macro group called mcrCourses
15.3.3 Use an unbound combo box to
automate search
As mentioned in Tutorial 8, a combo box has no
intrinsic search capability. However, the idea of scan-
ning a short list of key values, selecting a value, and
having all the information associated with that record
pop on to the screen is so basic that in Access ver-
sion 7.0 and above, this capability is included in the
combo box wizard. In this tutorial, we will look at a
or simplyuse the builder to set the arguments
You can
type in the names of the fields.
couple of different means of creating a combo boxes
for search from scratch.
of the control is changed by the user. As a result, the 15.3.3.1 Manual search in Access
After Update event is often used to trigger data verifi- To see how Access searches for records, do the fol-
cation procedures and “auto-fill” procedures like the lowing:
one you are creating here. • Open your frmDepartments form.



• Move to the field on which you want to search • Set the Enabled property of DeptCode to No (the
(e.g., DeptCode); user should never be able to change the key val-
• Select Edit Find (or press Control-F); ues of existing records).
• Fill out the search dialog box as shown in
15.3.3.3 Creating the unbound combo box
Figure 15.9.
The key thing to remember about the combo box
In the dialog box, you specify what to search for used to specify the search criterion is that it has
(usually a key value) and specify how Access should
nothing to do with the other fields or the underlying
conduct its search. When you press Find First, table. As such, it should be unbound.
Access finds the first record that matches your
• Create an unbound combo box in the form
search value and makes it the current record (note
header, as shown in Figure 15.10.
that if you are searching on a key field, the first • Change the Name property of the combo box to
matching record is also the only matching record).
cboDeptCode.
15.3.3.2 Preliminaries • The resulting combo box should resemble that
To make this more interesting, assume that the frm- shown in Figure 15.11.
Departments form is for viewing editing existing
When you create an unbound combo box,
departmental information (rather than adding new
Access gives it a default name (e.g.,
departments). To enforce this limitation, do the fol-
Combo5). You should do is change this to
lowing:
something more descriptive (e.g., cboDept-
• Set the form’s Allow Additions property to No.



FIGURE 15.9: Search for a record using the “find” dialog box.

the field you wishtoto
Move the cursor
search and invoke
the search box
using Control-F.

and setthe value you wish to find
Enter
the other search
parameters as required.

Limit the search to the current
field (i.e., the field with the
focus when the search box was
opened).

(or only) record that matches the
Press Find First to move to the first

search condition.



FIGURE 15.10: Create an unbound combo box.

down themake roomfor the detail
Drag
to
separator
in the form
header

selecting the combocombo boxand
Create an unbound
box tool
by

clicking in the header area.

Use the wizard in the usual way
to get a list of valid DeptCode
values and descriptions. The
bound column for the combo box
should be DeptCode.

its value has to bebox is unbound,
Since the combo
stored for later
use rather than stored in a field.



15.3.3.4 Automating the search procedure
FIGURE 15.11: An unbound combo box.
using a macro
When we implement search functionality with a
combo box, only two things are different from the
manual search in Figure 15.9:
1. the search dialog box does not show up, and
2. the user selects the search value from the combo
box rather than typing it in.
The basic sequence of actions, however, remains
Although the DeptCode column has been the same. As a result, the answer to the “what” ques-
hidden, it is the “bound” column. As a result,
the value of the combo box as it appears here tion is the following:
is “COMM”, not “Commerce and ...” 1. Move the cursor to the DeptCode field (this
allows the “Search Only Current Field” option to
Code). The advantage of the prefix cbo is be used, thereby drastically cutting the search
that it allows you to differentiate between the time).
bound field DeptCode and the unbound 2. Invoke the search feature using the current value
combo box. of cboDeptCode as the search value.



3. Move the cursor back to cboDeptCode or some
FIGURE 15.13: Fill in the arguments for the
other field.
FindRecord action.
The only problem with this procedure is that the
DeptCode text box is disabled. As a result, you must
include an extra step at the beginning of the macro
mcrSearch.FindDepartment.
Create a named macro called

to set its Enabled property to Yes and another at the
end of the macro to return it to its original state.
• Create a new macro called mcrSearch.Find-
Department.
• Use the SetValue action to set the Dept-
Code.Enabled property to Yes. This can be
done using the expression builder, as shown in
Figure 15.12.
• Use the GotoControl action to move the cursor Since Value is
the default
to the DeptCode text box. Note that this action property, its use
will fail if the destination control is disabled. is optional.
• Use the FindRecord action to implement the
search as shown in Figure 15.13.
equalsthe action arguments. Dothe combo box.
Enter
sign before the name of
not forget the



FIGURE 15.12: Use the builder to specify the name of the property to set.

expressionItem argument, down
To set the
builder to drill
use the
to the correct form.

The middle pane shows all the
objects on the form including
labels and buttons (hence the
need for a good naming
convention).

(cboDeptCode) from thebox
Select the unbound combo
middle
pane. A list of properties for the
selected object is displayed in the
pane on the right.



Access interprets any text in the Find What 15.3.4 Using Visual Basic code instead of
argument as a literal string (i.e., quotation a macro
marks would not be required to find COMM). To Instead of attaching a macro to the After Update
use an expression (including the contents of a
event, you can attach a VBA procedure. The VBA
control) in the Find What argument, you must procedure is much shorter than its macro counter-
precede it with an equals sign (e.g.,
part:
=[cboDeptCode].
1. a copy (clone) of the recordset underlying the
• You cannot disable a control if it has the focus. form is created,
Therefore, include another GotoControl action 2. the FindFirst method of this recordset is used
to move the cursor to cboDeptCode before set- to find the record of interest.
ting DeptCode.Enabled = No. 3. the “bookmark” property of the clone is used to
• Attach the macro mcrSearch.FindDepart- move to the corresponding bookmark for the
ment to the After Update event of the cboDept- form.
Code combo box. To create a VBA search procedure, do the following:
• Test the search feature. • Change the After Update event of cboDeptCode
to “Event Procedure”.
• Press the builder ( ) to create a VBA subrou-
tine.


15. Advanced Triggers Application to the assignment

• Enter the two lines of code below, as shown in a non-human-readable data type and therefore is
Figure 15.14. not of much use unless it is used in the manner
Me.RecordsetClone.FindFirst shown here. Setting the Bookmark property of a
“DeptCode = ‘” cboDeptCode “'” record makes the record with that bookmark the
Me.Bookmark = current record. In the example above, the book-
Me.RecordsetClone.Bookmark mark of the records underlying the form is set to
This program consists of a number of interesting ele- equal the bookmark of the clone. Since the clone
ments: had its bookmark set by the search procedure,
• The property Me refers to the current form. You this is equivalent to searching the recordset
can use the form's actual name, but Me is much underlying the form.
faster to type.
• A form’s RecordsetClone property provides a 15.4 Application to the assignment
means of referencing a copy of the form's under-
lying recordset. 15.4.1 Triggers to help the user
• The FindFirst method is straightforward. It • Create a trigger on your order form that sets the
acts, in this case, on the clone. actual selling price of a product to its default
• Every recordset has a bookmark property that price. This allows the user to accept the default
uniquely identifies each record. A bookmark is price or enter a new price for that particular trans-
like a “record number”, except that it is stored as action (e.g., the item could be damaged). You will



FIGURE 15.14: Implement the search feature using a short VBA procedure.

referencethe After Update event to
Change
an event procedure.

editor.the builder button to invoke the VBA
Press

Access automatically names the
subroutine. Enter the two lines of code.



have to think carefully about which event to Section 10.4). The problem is updating the Back-
attach this macro to. Orders table itself because two different situations
• Create a trigger on your order form that calcu- have to be considered:
lates a suggested quantity to ship and copies this 1. A record for the particular customer-product
value into the quantity to ship field. The sug- combination exists in the BackOrders table --
gested value must take into account the amount If a backorder record exists for a particular cus-
ordered by the customer, any outstanding backo- tomer and a particular product, the quantity field
rders for that item by that customer, and the cur- of the record can be added-to or subtracted-from
rent quantity on hand (you cannot ship what you as backorders are created and filled.
do not have). The user should be able to override 2. A customer-product record does not exist in
this suggested value. (Hint: use the MinValue() the BackOrders table -- If the particular cus-
function you created in Section 12.5.) tomer has never had a backorder for the product
• Provide you customer and products forms with in question, then there is no record in the Back-
search capability. Orders table to update. If you attempt to update
a nonexistent record, you will get an error.
15.4.2 Updating the BackOrders table
What is required, therefore, is a means of determin-
Once a sales order is entered into the order form, it ing whether a record already exists for a particular
is a simple matter to calculate the amount of each customer-product combination. If a record does
product that should be backordered (you did this in exist, then it has to be updated; if a record does not



exist, then one has to be created. This is simple (see Section 15.3.2.4 to review renaming
enough to talk about, but more difficult to implement fields in queries).
in VBA. As a result, you are being provided with a
shortcut function called UpdateBackOrders() Note that if the backordered quantity is positive,
that implements this logic. items are backordered. If the backordered quantity is
negative, backorders are being filled. If the backor-
The requirements for using the UpdateBackO-
dered quantity is zero, no change is required and
rders() function are outlined in the following sec-
these records should no be included in the results of
tions:
the query.
15.4.2.1 Create the pqryItemsToBackOrder
15.4.2.2 Import the shortcut function
query
Import the Visual Basic for Applications (VBA) mod-
If you have not already done so, create the pqry-
ule containing the code for the
ItemsToBackOrder query described in
UpdateBackOrders() function. This module is
Section 10.4. The UpdateBackOrders() proce-
contained in an Access database called
dure sets the parameter for the query and then cre-
BOSC_Vx.mdb that you can download from the
ates a recordset based on the results.
course home page.
If you did not use the field names OrderID, • BOSC_V2.mdb is for those running Access ver-
and ProductID in your tables, you must use sion 2.0. To import the module, select File
the calculated field syntax to rename them



Import, choose BOSC_V2.mdb, and select Mod- ers, and Products. If any of your tables or fields
ule as the object type to import. are named differently, an error occurs. To eliminate
• BOSC_V7.mdb is for those running Access ver- these errors, you can do one of two of things:
sion 7.0 or higher. To import the module, select 1. Edit the VBA code. Use the search-and-replace
File Get External Data Import, choose feature of the module editor to replace all
BOSC_V7.mdb, and select Module as the object instances of field names in the supplied proce-
type to import. dures with your own field names. This is the rec-
15.4.2.3 Use the function in your application ommended approach, although you need an
adequate understanding of how the code works
The general syntax of the function call is:
UpdateBackOrders(OrderID, CustomerID). in order to know which names to change.
2. Change the field names in your tables (and all
The OrderID and CustomerID are arguments and
queries and forms that reference these field
they both must be of the type Long Integer. If this names). This approach is not recommended.
function is called properly, it will update all the backo-
rdered items returned by the parameter query. 15.4.3 Understanding the
15.4.2.4 Modifying the UpdateBackOrders() UpdateBackOrders() function
function The flowchart for the UpdateBackOrders() func-
The UpdateBackOrders() function looks for spe- tion is shown in Figure 15.15. This function repeat-
cific fields in three tables: BackOrders, Custom- edly calls a subroutine, BackOrderItem, which



updates or adds the individual items to the BackO- FIGURE 15.15: Flowchart for
rders table. The flowchart for the BackOrderItem UpdateBackOrders().
subroutine is shown in Figure 15.16.
There are easier and more efficient ways of imple- start

menting routines to update the BackOrders table.
Although some amount of VBA code is virtually inev- run pqryItemsToBackOrder
to get list of items to backorder
itable, a great deal of programming can be elimi-
nated by using parameter queries and action
queries. Since queries run faster than code in is yes
the list
Access, the more code you replace with queries, the empty?
error message stop
better.
no
To get full marks for the backorders aspect of
the assignment, you have to create a more do until end of list
elegant alternative to the shortcut supplied
here. call BackOrderItems
(CustID,ProductID,Qty)

stop



FIGURE 15.16: Flowchart for the BackOrderItem subroutine.

start

search BackOrders table for
matching CustID ProductID
yes

yes check Products table to
ensure valid ProductID
found? update Qty stop

no no
check Customer table to valid? error message stop
ensure valid CustID
yes

no add new record with
CustID, ProductID Qty
valid? error message stop

stop



15.4.4 Annotated source code for the MsgBox “Back order cannot be processed:
backorders shortcut module. order contains no items”
Exit Sub
In the following sections, the two procedures in the
End If
shortcut module are examined. In each case, the
Do Until rsBOItems.EOF
code for the procedure is presented followed by
Call BackOrderItem(lngCustID,
comments on specific lines of code.
rsBOItems!ProductID, rsBOItems!Qty)
15.4.4.1 The UpdateBackOrders() function rsBOItems.MoveNext
Function UpdateBackOrders(ByVal Loop
lngOrdID As Long, ByVal lngCustID As rsBOItems.Close
Long) End Function
15.4.4.2 Explanation of the
Dim rsBOItems As Recordset UpdateBackOrders() function
dbCurr.QueryDefs!pqryItemsToBackOrder.
Parameters!pOrderID = lngOrdID Function UpdateBackOrders(ByVal lngOr-
Set rsBOItems = dID As Long, ByVal lngCustID As Long) —
dbCurr.QueryDefs!pqryItemsToBackOrder This statement declares the function and its parame-
.OpenRecordset() ters. Each item in the parameter list contains three
If rsBOItems.RecordCount = 0 Then elements: ByVal or ByRef (optional), the variable's
name, and the variable's type (optional). The ByVal



keyword simply means that a copy of the variables Dim rsBOItems As Recordset — In this decla-
value is passed the subroutine, not the variable ration statement, a pointer to a Recordset object is
itself. As a result, variables passed by value cannot declared. This recordset contains a list of all the
be changed by the sub-procedure. In contrast, if a items to add to the BackOrders table.
variable is passed by reference (the default), its dbCurr.QueryDefs!pqryItemsToBackOrder
value can be changed by the sub-procedure. .Parameters!pOrderID = lngOrdID — This
Set dbCurr = CurrentDb — Declaring a vari- one is a bit tricky: the current database (dbCurr)
able and setting it to be equal to something are dis- contains a collection of objects called QueryDefs
tinct activities. In this case, the variable dbCurr (these are what you create when you use the QBE
(which is declared in the declarations section) is set query designer). Within the collection of QueryDefs,
to point to a database object. Note that the database there is one called pqryItemsToBackOrder
object is not created, it already exists. (which you created in Section 15.4.2.1).
CurrentDb is a function supported in Access ver- Within every QueryDef, there is a collection of zero
sion 7.0 and higher that returns a reference to the or more Parameters. In this case, there is one called
current database. In Access version 2.0, this function pOrderID and this sets the value of the parameter
does not exist and thus the current database must to the value of the variable lngOrderID (which was
be found by starting at the top level object in the passed to the function as a parameter).
Access DAO hierarchy, as discussed in Set rsBOItems = dbCurr.QueryDefs!pqry-
Section 14.3.1. ItemsToBackOrder.OpenRecordset() — Here



is another set statement. In this one, the variable MsgBox “Back order cannot be processed:
rsBOItems is set to point at a recordset object. order contains no items” — The MsgBox
Unlike the current database object above, however, statement pops up a standard message box with an
this recordset does not yet exist and must be created Okay button in the middle.
by running the pqryItemsToBackOrder parame- Exit Sub — If this line is reached, the list contains
ter query. no items. As such, there is no need to go any further
OpenRecordset is a method that is defined for in this subroutine.
objects of type TableDef or QueryDef that creates an End If — The syntax for If… Then… Else… state-
image of the data in the table or query. Since the ments requires an End If statement at the end of
query in question is a parameter query, and since the the conditional code. That is, everything between the
parameter query is set in the previous statement, the If and the End If executes if the condition is true;
resulting recordset consists of a list of backordered otherwise, the whole block of code is ignored.
items with an order number equal to the value of
Do Until rsBOItems.EOF — The EOF property
pOrderID.
of a recordset is set to true when the “end of file” is
If rsBOItems.RecordCount = 0 Then — The encountered.
only thing you need to know at this point about the
Call BackOrderItem(lngCustID, rsBOI-
RecordCount property of a recordset is that it returns
tems!ProductID, rsBOItems!Qty) — A sub-
zero if the recordset is empty.
routine is used to increase the modularity and



readability of this function. Note the way in which the 15.4.4.3 The BackOrderItem() subroutine
current values of ProductID and Qty from the Sub BackOrderItem(ByVal lngCustID As
rsBOItems Recordset are accessed. Long, ByVal strProdID As String, ByVal
rsBOItems.MoveNext — MoveNext is a method intQty As Integer)
defined for recordset objects. If this is forgotten, the
EOF condition will never be reached and an infinite Dim strSearch As String
Dim rsBackOrders As Recordset
loop will be created. In VBA, the Escape key is usu-
Set rsBackOrders =
ally sufficient to stop an infinite loop.
dbCurr.OpenRecordset(“BackOrders”,
Loop — All Do While/Do Until loops must end dbOpenDynaset)
with the Loop statement. strSearch = “CustID = “ lngCustID “
rsBOItems.Close — When you create a new AND ProductID = ' strProdID “'”
object (such as a Recordset using the Open- rsBackOrders.FindFirst strSearch
Recordset method), you should close it before exit- If rsBackOrders.NoMatch Then
ing the procedure. Note that you do not close Dim rsCustomers As Recordset
dbCurr because you did not open it. Set rsCustomers =
dbCurr.OpenRecordset(“Customers”,
End Function — All functions/subroutines need dbOpenDynaset)
an End Function/End Sub statement. strSearch = “CustID = “ lngCustID
rsCustomers.FindFirst strSearch



If rsCustomers.NoMatch Then rsBackOrders!Qty = intQty
MsgBox “An invalid Customer ID number rsBackOrders.Update
has been passed to BackOrderItem” Else
Exit Sub rsBackOrders.Edit
End If rsBackOrders!Qty = rsBackOrders!Qty +
Dim rsProducts As Recordset intQty
Set rsProducts = rsBackOrders.Update
dbCurr.OpenRecordset(“Products”, End If
dbOpenDynaset) End Sub
strSearch = “ProductID = ' strProdID
“'” 15.4.4.4 Explanation of the BackOrderItem()
rsProducts.FindFirst strSearch subroutine
If rsProducts.NoMatch Then Since many aspects of the language are covered in
MsgBox “An invalid Product ID number the previous subroutine, only those that are unique
has been passed to BackOrderItem” to this subroutine are explained.
Exit Sub Set rsBackOrders = dbCurr.OpenRecord-
End If set(“BackOrders”, dbOpenDynaset) — The
rsBackOrders.AddNew OpenRecordset method used here is the one
rsBackOrders!CustID = lngCustID defined for a Database object. The most important
rsBackOrders!ProductID = strProdID argument is the source of the records, which can be



a table name, a query name, or an SQL statement. do this, single quotes are used within the search
The dbOpenDynaset argument is a predefined con- string.
stant that tells Access to open the recordset as a rsBackOrders.FindFirst strSearch —
dynaset. You don't need to know much about this FindFirst is a method defined for Recordset
except that the format of these predefined constants objects that finds the first record that meets the crite-
is different between Access version 2.0 and version ria specified in the method's argument. Its argument
7.0 and higher. In version 2.0, constants are of the is the text string stored in strSearch.
form: DB_OPEN_DYNASET.
If rsBackOrders.NoMatch Then — The
strSearch = “CustID = ” lngCustID “ NoMatch property should always be checked after
AND ProductID = ’” strProdID “'” — searching a record set. Since it is a Boolean variable
A string variable has been used to break the search (True / False) it can be used without an comparison
process into two steps. First, the search string is operator.
constructed; then the string is used as the parameter
rsBackOrders.AddNew — Before information can
for the FindFirst method. The only tricky part here
be added to a table, a new blank record must be cre-
is that lngCustID is a long integer and strProdID
ated. The AddNew method creates a new empty
is a string. The difference is that the value of str-
record, makes it the active record, and enables it for
ProdID has to be enclosed in quotation marks when
editing.
the parameter is passed to the FindFirst method. To



rsBackOrders!CustID = lngCustID — Note
the syntax for changing a variable’s value. In this
case, the null value of the new empty record is
replaced with the value of a variable passed to the
subroutine.
rsBackOrders.Update — After any changes are
made to a record, the Update method must be
invoked to “commit” the changes. The AddNew /
Edit and Update methods are like bookends
around changes made to records.
rsBackOrders.Edit — The Edit method allows
the values in a record to be changed. Note that these
changes are not saved to the underlying table until
the Update method is used.


Ms access tutorials

More Related Content

Similar to Ms access tutorials (20)

Ms access tutorials