Db Triggers05ch

Enhanced Guide to Oracle8i Chapter 5: Advanced PL/SQL Programming

Anonymous PL/SQL Programs Write code in text editor, execute it in SQL*Plus Code can be stored as text in file system Program cannot be called by other programs, or executed by other users Cannot accept or pass parameter values

Named PL/SQL Programs Can be created: Using text editor & executed in SQL*Plus Using Procedure Builder Can be stored: As compiled objects in database As source code libraries in file system Can be called by other programs Can be executed by other users

Named Program Locations Server-side Stored in database as database objects Execute on the database server Client-side Stored in the client workstation file system Execute on the client workstation

Named Program Types Program Units (client or server-side) Procedures Functions Libraries (client-side) Packages (client or server-side) Triggers (server-side)

Program Units Procedures Can receive and pass multiple parameter values Can call other program units Functions Like procedures, except they return a single value

Variables used to pass data values in/out of program units Declared in the procedure header Parameter values are passed when the procedure is called from the calling program Parameters

Parameter Modes IN Incoming values, read-only OUT Outgoing values, write-only IN OUT Can be both incoming and outgoing

Creating a Procedure CREATE OR REPLACE PROCEDURE procedure_name ( parameter1 mode datatype, parameter2 mode datatype , … ) IS | AS local variable declarations BEGIN program statements EXCEPTION exception handlers END; header body

Executing a Procedure EXECUTE procedure_name ( parameter1_value , parameter2_value , …);

Formal parameters: declared in procedure header Actual parameters: values placed in parameter list when procedure is called Values correspond based on order Parameter Types Procedure Header: PROCEDURE calc_gpa (s_id IN NUMBER, term_id IN NUMBER, gpa OUT NUMBER); Procedure Call: calc_gpa (current_s_id, 4, current_gpa); Formal Parameters Actual Parameters

Debugging Named Program Units in SQL*Plus Isolate program lines causing errors and then fix them Use SHOW ERRORS command to view compile error details Use DBMS_OUTPUT.PUT_LINE commands to view intermediate values and track program flow

Creating a Function CREATE OR REPLACE FUNCTION function_name ( parameter1 mode datatype, parameter2 mode datatype , … ) RETURN function_return_data_type IS local variable declarations BEGIN program statements RETURN return_value ; EXCEPTION exception handlers RETURN EXCEPTION_NOTICE; END; header body

Function Syntax Details RETURN command in header specifies data type of value the function will return RETURN command in body specifies actual value returned by function RETURN EXCEPTION_NOTICE instructs the function to display the except notice in the calling program

Calling a Function Can be called from either named or anonymous PL/SQL blocks Can be called within SQL queries return_value := function_name ( parameter1_value, parameter2_value , …);

Stored Program Unit Object Privileges Stored program units exist as objects in your database schema To allow other users to use your units, you must grant them EXECUTE privileges GRANT EXECUTE ON unit_name TO username ;

Using Stored Program Units That Belong to Other Users You must have been granted the privilege to use it You must preface the unit name with the owner’s username return_value := LHOWARD.my_function TO_DATE(’07/14/1958’, ‘MM/DD/YYYY’);

Using Procedure Builder to Create Named Program Units Procedures and functions created in Notepad/SQL*Plus are always server-side Stored in the database Executed on the database server Procedure Builder can be used to create client-side libraries of procedures and functions Stored in the client file system Executed on the client

Procedure Builder Client-Side File Types .pls Single program unit Uncompiled source code Can only be opened/modified in Procedure Builder .pll Library of procedures or functions Compiled code Can be referenced in other Developer applications (Forms, Reports)

Procedure Builder Interface Object Navigator Window PL/SQL Interpreter Window command prompt pane source code pane

Program Unit Editor Interface Button bar Procedure list Procedure template Status line Source code pane

Creating Client-Side Objects in Procedure Builder Client-side program unit source code Create program unit in Program Unit Editor, export text to .pls file Client-side library Click File, click Save As, and specify to save library .pll file in file system

Executing a Procedure in Procedure Builder Load program unit as a top-level Program Unit object Type the procedure name and parameter list values at the command prompt

Set a breakpoint on the program line where execution will pause Single-step through the program lines and examine current variable values Global variables Stack (local) variables View program execution path Using the PL/SQL Interpreter to Find Runtime Errors

Setting a Breakpoint Load program unit in PL/SQL Interpreter window Double-click line to create breakpoint Breakpoint

Viewing Program Variable Values During Execution Variable values Execution arrow

Strategy For Using the PL/SQL Interpreter Debugger Run the program, and determine which line is causing the run-time error Run the program again, and examine variable values just before the error occurs to determine its cause

Calling Procedures From Other Procedures Use procedure name followed by parameter list procedure_name ( parameter1_value , parameter2_value , …);

Creating Server-Side Objects in Procedure Builder Stored program units Drag program unit from top-level node in Procedure Builder to Program Units node under Database node Libraries Click File, click Save As, and specify to save library in database Regardless of storage location, PL/SQL libraries ALWAYS execute on client

Program Unit Dependencies Object dependencies Program units are dependent on the database objects they reference (tables, views, sequences, …) Procedure dependencies Program units are dependent on other program units they call

Direct and Indirect Dependencies Direct dependency Object or program is directly called or referenced Indirect dependency Object or program is called or referenced by a subprogram

Direct and Indirect Dependencies Direct Dependency Indirect Dependency CREATE_ NEW_ ORDER CUST_ORDER CREATE_ NEW_ ORDER_LINE ORDER_LINE ORDER_ID_ SEQUENCE ORDER_ID_ SEQUENCE

Invalidation If an object or program on which a program has a dependency is changed, the program is invalidated , and must be recompiled

Packages Server-side code library Can contain: Global variable declarations Cursors Procedures Functions

Differences Between Packages and Libraries Libraries have to be explicitly attached to applications, while packages are always available to be called by applications Libraries always execute on client Packages always execute on server

Package Components Specification Used to declare all public variables, cursors, procedures, functions Body Contains underlying code for procedures and functions Rationale: Specification is visible to users, gives details on how to use Body is not visible, users don’t care about details

Creating a Package Specification in SQL*Plus CREATE OR REPLACE PACKAGE package_name IS --public variables variable_name datatype ; --program units PROCEDURE procedure_name ( parameter_list ); FUNCTION function_name ( parameter_list ); END;

Creating a Package Specification in SQL*Plus

Creating a Package Body in SQL*Plus CREATE OR REPLACE PACKAGE BODY package_name IS private variable declarations program unit blocks END;

Creating a Package Body in SQL*Plus

Calling a Program Unit That Is In a Package Preface the program unit name with the package name PACKAGE_NAME . program_unit_name ( parameter_list ); Example: DBMS_OUTPUT.PUT_LINE(‘Hello World’);

Overloading Program Units in Packages Overloading Multiple program units have the same name, but accept different input parameters Allows user to use the same command to perform an action but pass different parameter values

Package Specification With Overloaded Procedures

Saving Packages as Database Objects Expand the Database Objects node so your username appears, and expand your username so the Stored Program Units node appears Drag the Package Specification and Package Body under the Stored Program Units node

Database Triggers Program units that are attached to a specific table Execute in response to the following table operations: INSERT UPDATE DELETE

Uses For Database Triggers Force related operations to always happen Sell an item, update QOH Create a table that serves as an audit trail Record who changes a student grade and when they change it

Creating Database Triggers Code is similar to all PL/SQL program unit blocks Database triggers cannot accept parameters

Defining Triggers To define a trigger, you must specify: Statement type that causes trigger to fire INSERT, UPDATE, DELETE Timing BEFORE or AFTER Level STATEMENT or ROW

Trigger Timing BEFORE: trigger fires before statement executes Example: for audit trail, records grade value before it is updated AFTER: trigger fires after statement executes Example: update QOH after item is sold

Trigger Levels ROW: trigger fires once for each row that is affected Example: when adding multiple order lines, update multiple inventory QOH values STATEMENT: trigger fires once, regardless of how many rows are updated Example: for audit trail, you just want to record that someone updated a table, but you don’t care how many rows were updated

Creating a Trigger in SQL*Plus CREATE OR REPLACE TRIGGER trigger_name [BEFORE|AFTER] [INSERT|UPDATE|DELETE] ON table_name [FOR EACH ROW] [WHEN (condition)] BEGIN trigger body END;

Creating a Statement-Level Trigger in SQL*Plus

Trigger Restrictions You can only create triggers on tables that you own You must have the CREATE TRIGGER system privilege You cannot execute a COMMIT command in a trigger

Row-Level Trigger Syntax WHEN (condition): Optional Specifies to fire only when a row satisfies a certain search condition Referencing old and new values in the trigger body: :OLD. field_name :NEW. field_name

Creating a Row-Level Trigger in SQL*Plus

Creating a Trigger in Procedure Builder In the Object Navigator Pane, expand the Database Objects node, expand your username, and select the table to which the trigger will be attached Create a new trigger Specify the trigger properties

Specifying Trigger Properties in Procedure Builder Timing Statement type Trigger name Field WHEN condition Trigger body Level

INSTEAD-OF Triggers Fire when a user issues a DML command associated with a complex view Normally, users cannot insert, update, or delete records associated with complex views that are created by joining multiple tables

Creating an INSTEAD-OF Trigger in SQL*Plus

Disabling and Dropping Triggers Syntax to drop a trigger: DROP TRIGGER trigger_name ; Syntax to enable or disable a trigger: ALTER TRIGGER trigger_name [ENABLE | DISABLE];

Oracle Built-In Packages Provide support for basic database functions Owned by the SYS database schema

Oracle Built-In Package Types Transaction processing Application development Database and application administration Internal support

Transaction Processing Packages Provide procedures to support transaction processing DBMS_ALERT: dynamically sends messages to other database sessions DBMS_LOCK: creates user-defined locks on tables and records DBMS_SQL: implements Dynamic SQL DBMS_TRANSACTION: provides procedures for transaction management

Application Development Packages Aid developers in creating and debugging PL/SQL applications DBMS_DESCRIBE: returns information about the parameters of any stored program unit DBMS_JOB: schedules PL/SQL named programs to run at specific times DBMS_OUTPUT: provides text output in PL/SQL programs in SQL*Plus DBMS_PIPE: sends messages to other database sessions DBMS_SESSION: dynamically changes the properties of a database session UTL_FILE: enables PL/SQL output to be written to a binary file

DBMS_JOB Package Enables PL/SQL named programs to be run at certain times Creates a job queue List of programs to be run, and times they are to be run

DBMS_PIPE Package Implements database pipes Used to transfer information among database sessions independently of transactions Sending a message Use the PACK_MESSAGE and SEND_MESSAGE procedures Receiving a message Use the RECEIVE_MESSAGE and UNPACK_MESSAGE procedures

Database and Application Administration Packages Support database administration tasks DBMS_APPLICATION_INFO: registers information about programs being run by individual user sessions DBMS_DDL: provides procedures for compiling program units and analyzing database objects DBMS_SHARED_POOL: used to manage the shared pool DBMS_SPACE: provides information for managing how data values are physical stored in the database DBMS_UTILITY: provides procedures for compiling all program units and analyzing all objects in a database schema

Internal Support Packages Provide underlying functionality of the Oracle database STANDARD: defines all built-in functions and procedures, database data types, and PL/SQL data types DBMS_SNAPSHOT: used to manage database snapshots DBMS_REFRESH: used to refresh snapshots DBMS_STANDARD: contains common functions of the PL/SQL language

Dynamic SQL Allows you to create SQL commands as text strings in PL/SQL programs, and validate the database objects at runtime Allows user to specify program inputs Supporting procedures are provided in the DBMS_SQL package

Creating Dynamic SQL Programs that Contain DML Commands Open the cursor that defines the memory area where processing is performed Define the SQL command as a text string, using placeholders for dynamic values Parse the SQL command Bind input variables to placeholders Execute the SQL command Close the cursor

Creating Dynamic SQL Programs that Contain DDL Commands Open the cursor that defines the memory area where processing is performed Define the SQL command as a text string You cannot define placeholders and dynamically bind values Parse the SQL command Close the cursor

Creating Dynamic SQL Programs that Contain SELECT Commands Open the cursor Define the SQL command as a text string using placeholders for dynamic values Parse the SQL command Bind input values to placeholders Define output variables Execute the query Fetch the rows Associate the fetched rows with the output variables Close the cursor

Using Dynamic SQL to Create an Anonymous PL/SQL Block Open the cursor Define the SQL command as a text string using placeholders for dynamic values Parse the SQL command Bind input and output values to placeholders Execute the query Retrieve values of output variables Close the cursor

Db Triggers05ch

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