SImple SQL

Structured Query Language
(SQL)

Cutajar & Cutajar

What is SQL?
 SQL stands for Structured Query Language. SQL is used to
communicate with a database.
 According to ANSI (American National Standards Institute), it is the
standard language for relational database management systems.
 SQL statements are used to perform tasks such as update data on
a database, or retrieve data from a database.
 Some common relational database management systems that use
SQL are: Oracle, Sybase, Microsoft SQL Server, Access, Ingres, etc.
 Although most database systems use SQL, most of them also have
their own additional proprietary extensions that are usually only
used on their system.
 However, the standard SQL commands such as "Select", "Insert",
"Update", "Delete", "Create", and "Drop" can be used to accomplish
almost everything that one needs to do with a database.

Databases 2

Table Basics
 A relational database system contains one or more objects called
tables.
 The data or information for the database are stored in these tables.
 Tables are uniquely identified by their names and are comprised of
columns and rows. Columns contain the column name, data type,
and any other attributes for the column.
 Rows contain the records or Weather
data for the columns. Here is a city state high low
sample table called "weather".
Phoenix Arizona 105 90
 city, state, high, and low are the Tucson Arizona 101 92
columns. The rows contain the
Flagstaff Arizona 88 69
data for this table:
San Diego California 77 60
Albuquerque New Mexico 80 72
Databases 3

Selecting Data

 The select statement is used to query the database
and retrieve selected data that match the criteria that
you specify. Here is the format of a simple select
statement:
select "column1" [,"column2",etc] from "tablename" [where "condition"];

 The column names that follow the select keyword
determine which columns will be returned in the
results. You can select as many column names that
you'd like, or you can use a "*" to select all columns.
Databases 4

Where & From
 The table name that follows the keyword from specifies the table
that will be queried to retrieve the desired results.
 The where clause (optional) specifies which data values or rows
will be returned or displayed, based on the criteria described after
the keyword where.
 Conditional selections used in the where clause:
 = Equal
 > Greater than
 < Less than
 >= Greater than or equal
 <= Less than or equal
 <> Not equal to
 LIKE (see next slide)
Databases 5

Like
 The LIKE pattern matching operator can also be used in
the conditional selection of the where clause.
 Like is a very powerful operator that allows you to select
only rows that are "like" what you specify.
 The percent sign "%" can be used as a wild card to
match any possible character that might appear before
or after the characters specified.
 For example:
select first, last, city from employee
where first LIKE 'Er%';
 This SQL statement will match any first names that start with
'Er'. Note: Strings must be in single quotes.
Databases 6

Sample Table
employee
first last id age city state
John Jones 99980 45 Payson Arizona
Mary Jones 99982 25 Payson Arizona
Eric Edwards 88232 32 San Diego California
Mary Ann Edwards 88233 32 Phoenix Arizona
Ginger Howell 98002 42 Cottonwood Arizona
Sebastian Smith 92001 23 Gila Bend Arizona
Gus Gray 22322 35 Bagdad Arizona
Mary Ann May 32326 52 Tucson Arizona
Erica Williams 32327 60 Show Low Arizona
Leroy Brown 32380 22 Pinetop Arizona
Elroy Cleaver 32382 22 Globe Arizona
Databases 7

Exercise
1. select first, last, city from employee;
2. select last, city, age from employee
where age > 30;
3. select first, last, city, state from employee
where first LIKE 'J%';
4. select * from employee;
5. select first, last, from employee
where last LIKE '%s';
6. select first, last, age from employee
where last LIKE '%illia%';
7. select * from employee where first = 'Eric';
Databases 8

Select statement exercises

 Write select statements to:
1. Display the first name and age for everyone that's in the
table.
2. Display the first name, last name, and city for everyone
that's not from Payson.
3. Display all columns for everyone that is over 40 years old.
4. Display the first and last names for everyone whose last
name ends in an "ay".
5. Display all columns for everyone whose first name equals
"Mary".
6. Display all columns for everyone whose first name contains
"Mary".

Databases 9

Creating Tables

 The create table statement is used to create a new
table. Here is the format of a create table
statement:
create table "tablename"
("column1" "data type" [constraint],
"column2" "data type" [constraint],
"column3" "data type" [constraint]);

Note: You may have as many columns as you'd like,
and the constraints are optional.

Databases 10

Example
create table employee
(first varchar(15), last varchar(20), age number(3),
address varchar(30), city varchar(20), state varchar(20));

 To create a new table, enter the keywords create table followed by the
table name, followed by an open parenthesis, followed by the first column
name, followed by the data type for that column, followed by any optional
constraints, and followed by a closing parenthesis. It is important to make
sure you use an open parenthesis before the beginning table, and a
closing parenthesis after the end of the last column definition. Make sure
you separate each column definition with a comma.
 All SQL statements should end with a ";".
 The table and column names must start with a letter and can be followed
by letters, numbers, or underscores - not to exceed a total of 30
characters in length.
 Do not use any SQL reserved keywords as names for tables or column
names (such as "select", "create", "insert", etc).
Databases 11

Data types

 Data types specify what the type of data can be for that particular
column. If a column called "Last_Name", is to be used to hold
names, then that particular column should have a "varchar"
(variable-length character) data type.
 Here are the most common Data types:

char(size) Fixed-length character string. Size is specified in parenthesis. Max 255 bytes.
varchar(size) Variable-length character string. Max size is specified in parenthesis.
number(size) Number value with a max number of column digits specified in parenthesis.
date Date value
Number value with a maximum number of digits of "size" total, with a
number(size,d)
maximum number of "d" digits to the right of the decimal.

Databases 12

Constraints
 What are constraints? When tables are created, it is
common for one or more columns to have constraints
associated with them.
 A constraint is basically a rule associated with a column
that the data entered into that column must follow.
 For example, a "unique" constraint specifies that no two
records can have the same value in a particular column.
They must all be unique.
 The other two most popular constraints are "not null"
which specifies that a column can't be left blank, and
"primary key". A "primary key" constraint defines a
unique identification of each record (or row) in a table.
Databases 13

Inserting into a Table
 The insert statement is used to insert or add a row of data into the table.
insert into "tablename"
(first_column,...last_column)
values (first_value,...last_value);

 The values that you enter will be held in the rows and they will match up
with the column names that you specify. Strings should be enclosed in
single quotes, and numbers should not.

 Example:
insert into employee (first, last, age, address, city, state)
values ('Luke', 'Duke', 45, '2130 Boars Nest', 'Hazard Co', 'Georgia');
Note: All strings should be enclosed between single quotes: 'string‘

 In this example the column name first will match up with the value 'Luke',
and the column name state will match up with the value 'Georgia'.

Databases 14

Insert statement exercises

 It is time to insert data into your new employee table.
 Your first three employees are the following:
 Jonie Weber, Secretary, 28, 19500.00
 Potsy Weber, Programmer, 32, 45300.00
 Dirk Smith, Programmer II, 45, 75020.00

 Enter these employees into your table first, and then insert at least 5 more of
your own list of employees in the table.

 After they're inserted into the table, enter select statements to:
1. Select all columns for everyone in your employee table.
2. Select all columns for everyone with a salary over 30000.
3. Select first and last names for everyone that's under 30 years old.
4. Select first name, last name, and salary for anyone with "Programmer" in their title.
5. Select all columns for everyone whose last name contains "ebe".
6. Select the first name for everyone whose first name equals "Potsy".
7. Select all columns for everyone over 80 years old.
8. Select all columns for everyone whose last name ends in "ith".

Databases 15

Updating Records

 The update statement is used to update or change
records that match a specified criteria. This is
accomplished by carefully constructing a where
clause.

update "tablename" set "columnname" = "newvalue"
[,"nextcolumn" = "newvalue2"...]
where "columnname" OPERATOR "value"
[and|or "column" OPERATOR "value"];

Databases 16

Examples

update phone_book set area_code = 623
where prefix = 979;

update phone_book
set last_name = 'Smith', prefix=555, suffix=9292
where last_name = 'Jones';

update employee set age = age+1
where first_name='Mary' and last_name='Williams';

Databases 17

Update statement exercises

 Issue an update statement for the following updates:
1. Jonie Weber just got married to Bob Williams. She has requested
that her last name be updated to Weber-Williams.
2. Dirk Smith's birthday is today, add 1 to his age.
3. All secretaries are now called "Administrative Assistant". Update all
titles accordingly.
4. Everyone that's making under 30000 are to receive a 3500 a year
raise.
5. Everyone that's making over 33500 are to receive a 4500 a year
raise.
6. All "Programmer II" titles are now promoted to "Programmer III".
7. All "Programmer" titles are now promoted to "Programmer II".

Databases 18

Deleting Records

 The delete statement is used to delete records or
rows from the table.
delete from "tablename"
where "columnname" OPERATOR "value"
[and|or "column" OPERATOR "value"];

Databases 19

Examples
delete from employee;
 Note: if you leave off the where clause, all records will be
deleted!
delete from employee where lastname = 'May';
delete from employee
where firstname = 'Mike' or firstname = 'Eric';

 To delete an entire record/row from a table, enter "delete
from" followed by the table name, followed by the where
clause which contains the conditions to delete. If you
leave off the where clause, all records will be deleted.

Databases 20

Drop a Table
 The drop table command is used to delete a table and
all rows in the table.
 To delete an entire table including all of its rows, issue
the drop table command followed by the tablename.
 drop table is different from deleting all of the records in
the table. Deleting all of the records in the table leaves
the table including column and constraint information.
Dropping the table removes the table definition as well
as all of its rows.
drop table "tablename"
Example:
drop table employee;
Databases 21

Advanced SELECT Statement

 The SELECT statement is used to query the database and
retrieve selected data that match the criteria that you specify.
 The SELECT statement has five main clauses to choose from,
although, FROM is the only required clause. Each of the clauses
have a vast selection of options, parameters, etc.
Here is the format of the SELECT statement:

SELECT [ALL | DISTINCT] column1[,column2]
FROM table1 [,table2]
[WHERE "conditions"]
[GROUP BY "column-list"]
[HAVING "conditions]
[ORDER BY "column-list" [ASC | DESC] ]

Databases 22

ALL and DISTINCT
 ALL and DISTINCT are keywords used to select either ALL
(default) or the "distinct" or unique records in your query
results. If you would like to retrieve just the unique records in
specified columns, you can use the "DISTINCT" keyword.
DISTINCT will discard the duplicate records for the columns you
specified after the "SELECT" statement: For example:

SELECT DISTINCT age FROM employee_info;

This statement will return all of the unique ages in the
employee_info table.

 ALL will display "all" of the specified columns including all of the
duplicates. The ALL keyword is the default if nothing is
specified.
Databases 23

Aggregate Functions

 MIN returns the smallest value in a given column
 MAX returns the largest value in a given column
 SUM returns the sum of the numeric values in a given column
 AVG returns the average value of a given column
 COUNT returns the total number of values in a given column
 COUNT(*) returns the number of rows in a table

 Aggregate functions are used to compute against a "returned
column of numeric data" from your SELECT statement.
 They basically summarize the results of a particular column of
selected data.

Databases 24

Examples
SELECT AVG(salary)
FROM employee;

 This statement will return a single result which contains the average value of
everything returned in the salary column from the employee table.

SELECT AVG(salary)
FROM employee;
WHERE title = 'Programmer';

 This statement will return the average salary for all employees whose title is
equal to 'Programmer'

SELECT Count(*)
FROM employees;

 This particular statement is slightly different from the other aggregate
functions since there isn't a column supplied to the count function. This
statement will return the number of rows in the employees table.

Databases 25

items_ordered
Sample customerid order_date item
10330 30-Jun-99 Pogo stick
quantity price
1 28

Tables
10101 30-Jun-99 Raft 1 58
10298 01-Jul-99 Skateboard 1 33
10101 01-Jul-99 Life Vest 4 125
10299 06-Jul-99 Parachute 1 1250
10339 27-Jul-99 Umbrella 1 4.5
10449 13-Aug-99 Unicycle 1 180.79
10439 14-Aug-99 Ski Poles 2 25.5
10101 18-Aug-99 Rain Coat 1 18.3
customers 10449 01-Sep-99 Snow Shoes
10439 18-Sep-99 Tent
1
1
45
88
customerid firstname lastname city state 10298 19-Sep-99 Lantern 2 29
10101 John Gray Lynden Washington 10410 28-Oct-99 Sleeping Bag 1 89.22
10298 Leroy Brown Pinetop Arizona 10438 01-Nov-99 Umbrella 1 6.75
10299 Elroy Keller Snoqualmie Washington 10438 02-Nov-99 Pillow 1 8.5
10315 Lisa Jones Oshkosh Wisconsin 10298 01-Dec-99 Helmet 1 22
10325 Ginger Schultz Pocatello Idaho 10449 15-Dec-99 Bicycle 1 380.5
10329 Kelly Mendoza Kailua Hawaii 10449 22-Dec-99 Canoe 1 280
10330 Shawn Dalton Cannon Beach Oregon 10101 30-Dec-99 Hoola Hoop 3 14.75
10338 Michael Howell Tillamook Oregon 10330 01-Jan-00 Flashlight 4 28
10339 Anthony Sanchez Winslow Arizona 10101 02-Jan-00 Lantern 1 16
10408 Elroy Cleaver Globe Arizona 10299 18-Jan-00 Inflatable Mattress 1 38
10410 Mary Ann Howell Charleston South Carolina 10438 18-Jan-00 Tent 1 79.99
10413 Donald Davids Gila Bend Arizona 10413 19-Jan-00 Lawnchair 4 32
10419 Linda Sakahara Nogales Arizona 10410 30-Jan-00 Unicycle 1 192.5
10429 Sarah Graham Greensboro North Carolina 10315 02-Feb-00 Compass 1 8
10438 Kevin Smith Durango Colorado 10449 29-Feb-00 Flashlight 1 4.5
10439 Conrad Giles Telluride Colorado 10101 08-Mar-00 Sleeping Bag 2 88.7
10449 Isabela Moore Yuma Arizona 10298 18-Mar-00 Pocket Knife 1 22.38
10449 19-Mar-00 Canoe paddle 2 40
10298 01-Apr-00 Ear Muffs 1 12.5
10330 19-Apr-00 Shovel 1 16.75

Databases 26

Review Exercises

1. Select the maximum price of any item ordered in the
items_ordered table. Hint: Select the maximum price
only.
2. Select the average price of all of the items ordered
that were purchased in the month of Dec.
3. What are the total number of rows in the
items_ordered table?
4. For all of the tents that were ordered in the
items_ordered table, what is the price of the lowest
tent? Hint: Your query should return the price only.

Databases 27

GROUP BY clause
 The GROUP BY clause will gather all of the rows together that contain data
in the specified column(s) and will allow aggregate functions to be
performed on the one or more columns. This can best be explained by an
example:
SELECT column1, SUM(column2)
FROM "list-of-tables"
GROUP BY "column-list";

 Let's say you would like to retrieve a list of the highest paid salaries in each
dept:
SELECT max(salary), dept
FROM employee
GROUP BY dept;

This statement will select the maximum salary for the people in each unique
department. Basically, the salary for the person who makes the most in
each department will be displayed. Their, salary and their department will
be returned.
Databases 28

Example
 Take a look at the items_ordered table. Let's say you
want to group everything of quantity 1 together,
everything of quantity 2 together, everything of quantity
3 together, etc. If you would like to determine what the
largest cost item is for each grouped quantity (all
quantity 1's, all quantity 2's, all quantity 3's, etc.), you
would enter:

SELECT quantity, max(price)
FROM items_ordered
GROUP BY quantity;
Databases 29

Review Exercises
1. How many people are in each unique state in the
customers table? Select the state and display the
number of people in each. Hint: count is used to count
rows in a column, sum works on numeric data only.
2. From the items_ordered table, select the item,
maximum price, and minimum price for each specific
item in the table. Hint: The items will need to be
broken up into separate groups.
3. How many orders did each customer make? Use the
items_ordered table. Select the customerid, number of
orders they made, and the sum of their orders.
Databases 30

HAVING clause

 The HAVING clause allows you to specify conditions
on the rows for each group - in other words, which
rows should be selected will be based on the
conditions you specify. The HAVING clause should
follow the GROUP BY clause if you are going to use it.

GROUP BY "column-list"
HAVING "condition";

Databases 31

Examples
 HAVING can best be described by example. Let's say you have an
employee table containing the employee's name, department,
salary, and age. If you would like to select the average salary for
each employee in each department, you could enter:

SELECT dept, avg(salary)
FROM employee
GROUP BY dept;

 But, let's say that you want to ONLY calculate & display the
average if their salary is over 20000:

SELECT dept, avg(salary)
FROM employee
GROUP BY dept
HAVING avg(salary) > 20000;
Databases 32

Review Exercises

1. How many people are in each unique state in the customers table
that have more than one person in the state? Select the state and
display the number of how many people are in each if it's greater
than 1.
2. From the items_ordered table, select the item, maximum price,
and minimum price for each specific item in the table. Only display
the results if the maximum price for one of the items is greater
than 190.00.
3. How many orders did each customer make? Use the items_ordered
table. Select the customerid, number of orders they made, and the
sum of their orders if they purchased more than 1 item.

Databases 33

ORDER BY clause
 ORDER BY is an optional clause which will allow you to
display the results of your query in a sorted order (either
ascending order or descending order) based on the
columns that you specify to order by.

ORDER BY "column-list" [ASC | DESC];

Databases 34

Examples
 This statement will select the employee_id, dept, name, age, and salary
from the employee_info table where the dept equals 'Sales' and will list the
results in Ascending (default) order based on their Salary.
ASC = Ascending Order – default, DESC = Descending Order

SELECT employee_id, dept, name, age, salary
FROM employee_info
WHERE dept = 'Sales'
ORDER BY salary;

 If you would like to order based on multiple columns, you must seperate the
columns with commas. For example:

SELECT employee_id, dept, name, age, salary
FROM employee_info
WHERE dept = 'Sales'
ORDER BY salary, age DESC;

Databases 35

Review Exercises

 Select the lastname, firstname, and city for all
customers in the customers table. Display the results
in Ascending Order based on the lastname.
 Same thing as exercise #1, but display the results in
Descending order.
 Select the item and price for all of the items in the
items_ordered table that the price is greater than
10.00. Display the results in Ascending order based
on the price.

Databases 36

Combining conditions and
Boolean Operators
 The AND operator can be used to join two or more conditions in
the WHERE clause. Both sides of the AND condition must be true in
order for the condition to be met and for those rows to be
displayed.
WHERE "condition1" AND/OR "condition2";

 The OR operator can be used to join two or more conditions in the
WHERE clause also. However, either side of the OR operator can
be true and the condition will be met - hence, the rows will be
displayed. With the OR operator, either side can be true or both
sides can be true.
Databases 37

Examples
 For example:
 SELECT employeeid, firstname, lastname, title, salary
FROM employee_info
WHERE salary >= 50000.00 AND title = 'Programmer';

 SELECT employeeid, firstname, lastname, title, salary
FROM employee_info
WHERE (salary >= 50000.00) AND (title = 'Programmer');
Although they are not required,
you can use paranthesis around
 SELECT firstname, lastname, title, salary your conditional expressions to
make it easier to read:
FROM employee_info
WHERE (title = 'Sales') OR (title = 'Programmer');

Databases 38

Review Exercises

1. Select the customerid, order_date, and item from
the items_ordered table for all items unless they are
'Snow Shoes' or if they are 'Ear Muffs'. Display the
rows as long as they are not either of these two
items.
2. Select the item and price of all items that start with
the letters 'S', 'P', or 'F'.

Databases 39

IN and BETWEEN Conditional
Operators
SELECT col1, SUM(col2)
WHERE col3 IN (list-of-values);

SELECT col1, SUM(col2)
WHERE col3 BETWEEN value1 AND value2;

One can also use NOT IN and NOT BETWEEN
to invert the selection.
Databases 40

Examples

 The IN clause:

SELECT employeeid, lastname, salary
FROM employee_info
WHERE lastname IN ('Hernandez', 'Jones', 'Roberts‘ );

 The BETWEEN clause:

SELECT employeeid, age, lastname, salary
FROM employee_info
WHERE age BETWEEN 30 AND 40;

Databases 41

Review Exercises

1. Select the date, item, and price from the
items_ordered table for all of the rows that have a
price value ranging from 10.00 to 80.00.
2. Select the firstname, city, and state from the
customers table for all of the rows where the state
value is either: Arizona, Washington, Oklahoma,
Colorado, or Hawaii.

Databases 42

Mathematical Operators
 ABS(x)
 + addition  SIGN(x)
 - subtraction  MOD(x,y)
 * multiplication  FLOOR(x)
 / division  CEILING(x) or CEIL(x)
 % modulo  POWER(x,y)
 ROUND(x)
 ROUND(x,d)
 For example:  SQRT(x)
SELECT round(salary), firstname
FROM employee_info

This statement will select the salary rounded to the nearest whole
value and the firstname from the employee_info table.

Databases 43

Non – Standard Functions
 ABS(x) returns the absolute value of x
 SIGN(x) returns the sign of input x as -1, 0, or 1 (negative, zero,
or positive respectively)
 MOD(x,y) modulo - returns the integer remainder of x divided by y
(same as x%y)
 FLOOR(x) returns the largest integer value that is less than or
equal to x
 CEILING(x) or CEIL(x) returns the smallest integer value that is
greater than or equal to x
 POWER(x,y) returns the value of x raised to the power of y
 ROUND(x) returns the value of x rounded to the nearest whole
integer
 ROUND(x,d) returns the value of x rounded to the number of
decimal places specified by the value d
 SQRT(x) returns the square-root value of x
Databases 44

Table Joins, a must
 All of the queries up until this point have been useful with the
exception of one major limitation - that is, you've been selecting
from only one table at a time with your SELECT statement. It is
time to introduce you to one of the most beneficial features of SQL
& relational database systems - the "Join". To put it simply, the
"Join" makes relational database systems "relational".
 Joins allow you to link data from two or more tables together into a
single query result-from one single SELECT statement.
 A "Join" can be recognized in a SQL SELECT statement if it has
more than one table after the FROM keyword.
 For example:
SELECT "list-of-columns"
FROM table1,table2
WHERE "search-condition(s)"
Databases 45

Example
 Customer_info(customer_number, firstname, lastname,
address, city, state, zip)
 Purchases(customer_number, date, item, price)

SELECT customer_info.firstname, customer_info.lastname,
purchases.item
FROM customer_info, purchases
WHERE customer_info.customer_number =
purchases.customer_number;

Databases 46

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