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Advanced SQL and PL/SQL Topics

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Guide to Oracle 10g 2

Overview of PL/SQL Stored Program Units

• Program unit – Self-contained group of program statements that

can be used within larger program

• Anonymous PL/SQL programs• Stored PL/SQL program units• Server-side program units• Client-side program units


Types of Oracle 10g Stored Program Units

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Creating Stored Program Units

• Procedure– Receive multiple input parameters

– Return multiple output values or return no output values

– Perform action such as inserting, updating, or deleting database records

• Function– Receive multiple input parameters

– Always returns single output value


Stored Program Unit Procedures

• CREATE_PROCEDURE command– Header

– Parameter declarations list

– Program unit body

– Exception section


Syntax to Create a Stored Program Unit Procedure

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Creating the Parameter Declarations List

• Defines parameters • Declares associated data types• Parameter mode

– IN

– OUT

– IN OUT


Creating a Stored Procedure in SQL*Plus

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Debugging Stored Program Units in SQL*Plus

• Similar to debugging any program• Identify program line causing error• SQL*Plus interpreter displays error warning

message– Does not automatically display compile error

messages and line locations

– Writes all compile errors to system table • Access using USER_ERRORS data dictionary view

• Execute SHOW ERRORS command


Calling a Stored Procedure

• Execute directly from SQL*Plus command line• Create separate PL/SQL program that contains

– Command to call stored procedure– Passes parameter values to procedure

• Calling stored procedure from SQL*Plus command line:EXECUTE procedure_name

(parameter1_value, parameter2_value, ...);


Passing Parameters to a Procedure

•IN The value of the parameter is passed into the procedure when the procedure is invoked. It is similar to read-only •OUT Any value the parameter has when it is called is ignored. When the procedure finishes, any value assigned to the parameter during its execution is returned to the calling environment. It is similar to write-only IN OUT This mode is a combination of both IN and OUT. The value of the parameter can be passed into the procedure when the procedure is invoked. It is then manipulated within the procedure and returned to the calling environment. It is similar to read-write

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Calling a Stored Procedure (continued)

• Variables passed for each parameter– Must be in same order as parameters appear in

parameter declarations list

• Calling stored procedure from separate PL/SQL program– Similar to calling stored procedure from SQL*Plus

command line

– Omit EXECUTE command– update_enrollment_grade(MA100, 12, B);


Creating a Stored Program Unit Function

• Use CREATE OR REPLACE FUNCTION command

• function_return_value_datatype – Defines data type that function returns

• return_value_variable – Declares variable that represents function return

value

• RETURN command


Commands to Create a Stored Program Unit Function

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Calling a Function

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

• Variables passed for parameter values– Must be in same order as parameters appear in

function declaration


Packages

• Code library containing related program units and variables

• Stored in database • Executes on database server• Grant other users privilege to use package

– Any PL/SQL program can reference package procedures and functions

• More functionality than PL/SQL libraries• More convenient to use than PL/SQL libraries


The Package Specification

• Also called package header• Declares public package objects, including:

– Variables – Cursors– Procedures– Functions

• Made public– Program units outside package can reference

package’s objects


The Package Specification (continued)

• Public variables– Visible to many different PL/SQL programs

– Values remain in memory even after programs that declare and reference them terminate

– Declare public variable in DECLARE section of package

• Same syntax used to declare private variable


General Syntax for a Package Specification

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• Declare variables and cursors in packages– Same syntax used in other PL/SQL programs

• Declare procedure syntax:PROCEDURE procedure_name

(parameter1 parameter1_data_type,

parameter2 parameter2_data_type, ...);



• Declare function syntax:FUNCTION function_name

(parameter1 parameter1_data_type,

parameter2 parameter2_data_type, ...)

RETURN return_datatype;


The Package Body

• Contains commands to create program units that package specification declares

• Must create specification before body• Optional• Variables declared at beginning of package body

– Private to package

• Each program unit in package specification must be defined


General Syntax for a Package Body

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The Package Body (continued)

• Create package using SQL*Plus• Create package specification in SQL*Plus• Create package body in SQL*Plus• Reference package objects syntax:

– package_name.item_name


The Package Body (continued)

• Package exists in user schema– Must grant permission to others– GRANT EXECUTE ON package_name TO username;


Database Triggers

• Program units – Execute in response to database events of inserting,

updating, or deleting record

• Different from form triggers• Useful for maintaining integrity constraints• Similar to other program units

– But cannot accept parameters


Database Trigger Properties

• Trigger timing– BEFORE

– AFTER

• Trigger statement– INSERT

– UPDATE

– DELETE


Database Trigger Properties (continued)

• Trigger level– Statement-level

– Row-level

• Reference value of field in current record – Both before and after triggering statement executes

•:OLD.fieldname•:NEW.fieldname


Creating Database Triggers

• Database trigger header• Trigger body


General Syntax to Create a Trigger in SQL*Plus

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Creating Database Triggers to Leave an Audit Trail for the Northwoods University ENROLLMENT Table

• Track when users insert, update, and delete table records

• Create trigger that leaves audit trail– Create one or more tables to store audit trail values

• Create database trigger in SQL*Plus• Create database trigger in Forms Builder


Disabling and Dropping Triggers

• Drop trigger when not needed:– DROP TRIGGER trigger_name;

• Disable trigger– Trigger still exists in user’s database schema

– No longer fires when triggering event occurs

– Syntax:•ALTER TRIGGER trigger_name [ENABLE | DISABLE];


Viewing Information About Triggers

• USER_TRIGGERS data dictionary view– Contains information about triggers

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