advanced sql and pl/sql topics

A Guide to Oracle9i 1

Advanced SQL And PL/SQL Topics

Chapter 9

A Guide to Oracle9i 2

Lesson A Objectives

• Learn how to create and use indexes• Become familiar with PL/SQL stored program units• Learn how to create server-side stored program units

in SQL*Plus• Learn how to use Forms Builder to create stored

program units

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Database Indexes

• Similar to an index in a book• Table with list of sorted data values and

corresponding physical location• Used to speed searches• Uses ROWID column to represent physical location• Primary key indexed automatically• Unlimited number allowed, but more indexes means

more processing time for action queries (insert, update, delete)

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Creating an Index

• Create index after table data is loaded• CREATE INDEX index_name ON tablename

(index_fieldname);• Convention for naming index: tablename_fieldname.

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Composite Index

• Contains multiple (up to 16) sorted columns• Used for queries with multiple search conditions• CREATE INDEX index_name ON

tablename(index_fieldname1, index_fieldname2, …);

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Viewing Index Information

• Use data dictionary view USER_INDEXES

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Dropping an Index

• If an index is no longer needed or does not improve performance, delete it

• DROP INDEX index_name;

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Use an Index When

• Table contains a large number of records (a rule of thumb is that a large table contains over 100,000 records)

• The field contains a wide range of values• The field contains a large number of NULL values• Application queries frequently use the field in a

search condition or join condition• Most queries retrieve less than 2% to 4% of the table

rows

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Do Not Use an Index When

• The table does not contain a large number of records• Applications do not use the proposed index field in a

query search condition• Most queries retrieve more than 2% to 4% of the

table records• Applications frequently insert or modify table data

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Overview of PL/SQL Stored Program Units

• Self-contained group of program statements that can be used within a larger program.

• Easier to conceptualize, design, and debug • Save valuable programming time because

you can reuse them in multiple database applications

• Other PL/SQL programs can reference them

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Overview of PL/SQL Stored Program Units

• Server-side program units — stored in the database as database objects and execute on the database server

• Client-side program units — stored in the file system of the client workstation and execute on the client workstation

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Types of Program Units

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Creating Stored Program Units• Procedure: a program unit that can receive multiple input parameters

and return multiple output values or return no output values• Function: a program unit that can receive multiple input parameters,

and always returns a single output value.

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Parameter Declarations List

• Defines the parameters and declares their associated data types

• Enclosed in parentheses• Separated by commas

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Parameter Declarations List

• Parameter mode describes how the program unit can change the parameter value:– IN - specifies a parameter that is passed to the program unit

as a read-only value that the program unit cannot change. – OUT - specifies a parameter that is a write-only value that

can appear only on the left side of an assignment statement in the program unit

– IN OUT - specifies a parameter that is passed to the program unit, and whose value can also be changed within the program unit

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Creating a Stored Procedure in SQL*Plus

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Debugging Stored Program Units in SQL*Plus

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Debugging Stored Program Units in SQL*Plus

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Calling a Stored Procedure

• From SQL*Plus command line:– EXECUTE procedure_name (parameter1_value,

parameter2_value, ...);

• From PL/SQL program:– Omit execute command

• Passing parameters (see Figure 9-13)

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Creating a Stored Program Unit Function

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Creating a Stored Program Unit Function

• Last command in function must be RETURN

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Calling a Function

• variable_name := function_name(parameter1, parameter2, ...);

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Using Forms Builder to Create Stored Procedures and Functions

• Create and test the program unit within a form• Save it as a stored program unit in your database

schema• Provides an enhanced development and debugging

environment:– Color-coded editor for entering and debugging program unit

commands– Displays compile error messages immediately– Use the Forms Debugger to step through program unit

commands and view how variable values change

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Using Forms Builder to Create Stored Procedures and Functions

• Create the procedure or function as a form program unit

• Test and debug the form program unit by calling it from commands within a form trigger

• Save the form program unit as a stored program unit in the database

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Lesson B Objectives

• Learn how to call stored procedures from other stored procedures and pass parameter values

• Create libraries• Create packages• Create database triggers

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Calling Stored Program Units from Other Stored Program Units

• Decompose applications into logical units of work and then write individual program units for each logical unit

• Code is in a single location• Developers do not need to rewrite program units that

already exist• References procedures must be declared first

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PL/SQL Libraries

• Operating system file that contains code for multiple related procedures and functions

• Attach a PL/SQL library to a form or report– Triggers within the form or report reference library’s procedures and

functions

• Store a PL/SQL library in the file system of the client workstation

• .pll extension - stands for “PL/SQL Library”

• Compile the library into a library executable file - .plx extension - stands for “PL/SQL Library Executable”

• Library places the commands for multiple related program units in a single location that developers can access and use

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Creating a PL/SQL Library

• Use Forms Builder to create libraries• Add form program units and stored program units to the library.

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Packages

• Another way to make PL/SQL program units available to multiple applications

• A code library that contains related program units and variables

• Stored in the database and executes on the database server

• Have more functionality than PL/SQL libraries:– Can create variables in packages

– Definitions for explicit cursors

– More convenient to use than PL/SQL libraries

– Available without explicitly attaching them to a form or report

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Package Specification

• Also called package header• Declares package objects, including

variables, cursors, procedures, and functions,• Use to declare public variables:

– Remain in memory after the programs that declare and reference them terminate

– Declared in the DECLARE section of a package– Referenced same as private variables

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Package Specification

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Package Header

• Package_name identifies the package– Must adhere to the Oracle Naming Standard

• Declare the package objects in any order• Package can consist of just variable

declarations, or it can consist of just procedure or function declarations

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Procedure and Function Declarations

• Declare a procedure:PROCEDURE procedure_name

(parameter1 parameter1_data_type,

parameter2 parameter2_data_type, ...);• Declare a function:

FUNCTION function_name

(parameter1 parameter1_data_type,

parameter2 parameter2_data_type, ...)

RETURN return_datatype;

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Package Body

• Contains the implementation of declared procedures and functions• Specification comes before body• Optional: sometimes a package contains only variable or cursor

declarations, and no procedure or function declarations• See Figure 9-35 for general syntax

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Package Body

• Package_name in the package body must be the same as package_name in the package specification

• Variables that you declare at the beginning of the package body are private to the package

• Each package program unit has its own declaration section and BEGIN and END statements

• Each program unit declared in the package body must have a matching program unit forward declaration in the package specification, with an identical parameter list

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Creating a Package Header in SQL*Plus

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Creating a Package Body in SQL*Plus

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Using Package Objects

• Must preface the item with the package name:– package_name.item_name.

• To grant other users the privilege to execute a package:– GRANT EXECUTE ON package_name TO

username;

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Creating a Package in Forms Builder

• Create a program unit of type Package Spec• Type the package specification in the PL/SQL editor• Create a program unit of type Package Body• Type package body in the PL/SQL editor• Compile package body and test using a form trigger• Save the package in the database for future use

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Database Triggers

• Program units that execute in response to the database events of inserting, updating, or deleting a record

• Different from form triggers• Useful for maintaining integrity constraints and audit

information• Cannot accept input parameters• Executes only when its triggering event occurs

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Trigger Properties

• Trigger timing:– Defines whether a trigger fires before or after the

SQL statement executes– Can have the values BEFORE or AFTER

• Trigger statement:– Defines the type of SQL statement that causes a

trigger to fire– Can be INSERT, UPDATE, or DELETE

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Trigger Properties

• Trigger level:– Defines whether a trigger fires once for each triggering

statement or once for each row affected by the triggering statement

– Can have the values ROW or STATEMENT– Statement-level triggers fire once, either before or after the

SQL triggering statement executes.– Row-level triggers fire once for each row affected by the

triggering statement

• Use :OLD.fieldname to reference previous value• Use :NEW.fieldname to reference changed value

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Creating Database Triggers

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Database Trigger Header

• Trigger_name must follow Oracle Naming Standard• Join statement types using the OR operator to fire for

multiple statement types (INSERT OR UPDATE)• WHEN (condition) clause:

– Trigger will fire only for rows that satisfy a specific search condition

– WHEN OLD.grade IS NOT NULL;

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Database Trigger Body

• Contains the commands that execute when the trigger fires

• PL/SQL code block that contains the usual declaration, body, and exception sections

• Cannot contain transaction control statements• Reference the NEW and OLD field values only in a

row-level trigger

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Trigger Use – Audit Trail

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Creating Audit Trigger in SQL*Plus

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Creating a Database Triggerin Forms Builder

• Use the Database Trigger Dialog Box to specify trigger properties

• Type trigger body into Trigger Body entry field

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Disabling and Dropping Triggers

• To remove a trigger:– DROP TRIGGER trigger_name;

• To disable/enable a trigger:– ALTER TRIGGER trigger_name [ENABLE |

DISABLE];

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Viewing Trigger Information

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Summary

• Database indexes store an ordered list of field values with corresponding ROWID

• Indexes are used to speed query performance• Stored program units are named PL/SQL blocks that

are saved• Procedures accept parameters and return 0,1, or

many values• Functions accept parameters and return exactly one

value

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Summary

• PL/SQL Library is a client-side file containing procedures and functions

• PL/SQL Package is a collection of public variables, cursors, procedures and functions stored in the DBMS

• Database triggers are PL/SQL blocks that are run in response to table changes

• Database triggers are used to enforce integrity constraints and track changes

• Forms Builder may be used as an IDE to develop functions, procedures, libraries, packages and triggers