Pls Ql 4 Sub Programs

8/22/2019 Pls Ql 4 Sub Programs

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Procedures and Functions


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CONFIDENTIAL Copyright 2008 Tech Mahindra Limited 2

Objectives

At the end of this session, you will be able to:

Understand subprograms and their need

Comprehend the difference between stored and unstoredsubprograms

Create and drop stored procedures and functions

Apply different parameter modes in subprograms

Understand and use procedures and functions that are local to

a stored subprogram Understand the different data dictionary views


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Agenda

Need for subprograms

Creating Stored Procedures

RAISE_APPLICATION_ERROR

Parameter Modes IN, OUT and IN OUT

Invoking stored procedures from SQL*Plus and PL/SQL Block

Examples of stored procedures and their invocation

Creating Stored Functions

Calling Stored Functions from different locations in DML and

SELECT Queries Local Procedures and Functions within a stored subprogram

Parameter passing mechanisms

Privileges related to functions and procedures

Dropping procedures and functions

Data dictionary views related to subprograms USER_OBJECTS

USER_SOURCE

USER_PROCEDURES

USER_ERRORS


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Subprograms in PL/SQL

PL/SQL blocks are anonymous, can not be called from otherPL/SQL blocks

Subprogram is a named PL/SQL block that could be either Stored Procedure, or

Stored Function, or

Package

Procedures and Functions behave similar to procedures of

other 3GLs


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Syntax for Creating a Procedure

Stored Procedure

A stored procedure is a named PL/SQL block that performs anaction. It is stored in the database as a database object forrepeated execution.

CREATE [ OR REPLACE ] PROCEDUREproc_name[(argument [mode] data type,argument [mode] data type,)]

-- PROCEDURES and FUNCTIONS may or may not acceptarguments

IS

Local PL/SQL variable declarations

BEGIN

Define action performed by the procedure

EXCEPTION

Handle exceptions, if any

END [ proc_name];

/


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RAISE_APPLICATION_ERROR Procedure

This procedure is used to display error messages along witherror numbers

ExampleRAISE_APPLICATION_ERROR(-20001, Invalid

Employee);

Note:

When called, RAISE_APPLICATION_ERROR ends a subprogram, rollsback any database changes it made, and returns a user-defined errormessage to the application

Error numbers should be between -20000 and -20999


7/32CONFIDENTIAL Copyright 2008 Tech Mahindra Limited 7

Parameters Modes in Procedures and Functions

Formal parameters can have three modes IN, OUT or IN OUT whichdecides the behavior of parameters

IN OUT IN OUT

Default parameter mode Must be specified Must be specified

Value is passed intosubprograms

Value is returned tothe callingenvironment

Value is passed intosubprogram andformatted/changedvalue is returned to thecalling environment

Formal parameter acts as

a constant inside asubprogram

Formal parameter

acts as a uninitializedvariable, as thesubprogram willassign value to it

Formal parameter acts

as a initialized variable,as the callingenvironment will pass avalue for it.

Actual parameter can bean expression, constantor initialized variable

Actual parametermust be a variable

Actual parameter mustbe a variable



IN Parameter: Example

CREATE OR REPLACE PROCEDURE

raise_salary (p_eno emp.empno%TYPE)

IS

vsal emp.sal%type;BEGIN

SELECT sal into vsal FROM emp WHERE empno=p_eno;

IF vsal



Invoking a Procedure

There are two methods to Invoke a Procedure

Invoke a Procedure from another PL/SQL block

e.g.

BEGIN

raise_salary(1002);

END;

/

Invoke a procedure from SQL*Plus environment by using

EXECUTE commande.g.

-- PROCEDURE call with parameter

EXECUTE raise_salary(1002);

Note: If no parameters are specified for a procedure, directly specify

procedure name without any parenthesis

e. g. EXECUTE procedure_name;



OUT Parameter: Example

CREATE OR REPLACE PROCEDURE query_emp

( p_eno IN emp.empno%TYPE,

p_name OUT emp.ename%TYPE,

p_sal OUT emp.sal%TYPE)

IS

BEGIN

SELECT ename , sal INTO p_name , p_sal FROM emp

WHERE empno = p_eno;

EXCEPTIONWHEN NO_DATA_FOUND THEN

RAISE_APPLICATION_ERROR(-20001, Employee does notexist);

END query_emp;

/


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Invoking a Procedure Having OUT Parameters

SQL> VARIABLE name VARCHAR2(20)

SQL> VARIABLE salary NUMBER

SQL> EXECUTE query_emp(1001,:name,:salary)

SQL> PRINT name salary

Note: The use of colon (:) is to reference the host variable inthe EXECUTE syntax


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IN OUT Parameter: Example

CREATE OR REPLACE PROCEDURE emp_salary_increase1

(p_salary IN OUT emp.sal%TYPE)

ISBEGIN

IF p_salary between 1000 and 2000 THEN

p_salary := p_salary * 1.2;

ELSIF p_salary between 2001 and 3000 THEN

p_salary := p_salary * 1.3;ELSIF p_salary > 3000 THEN

p_salary := p_salary* 1.4;

END IF;

EXCEPTION

WHEN OTHERS THENDBMS_OUTPUT.PUT_LINE(SQLERRM);

END;

/


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IN OUT Parameter (Contd.)

This PL/SQL block shows how to execute the above'emp_salary_increase' procedure

DECLARE

CURSOR updated_sal IS SELECT empno, sal FROM emp;

pre_sal emp.sal%TYPE;

BEGIN

FOR emp_rec IN updated_sal LOOPpre_sal := emp_rec.sal;

emp_salary_increase1 (emp_rec.sal);

DBMS_OUTPUT.PUT_LINE(' The salary of ' ||

emp_rec.empno ||' will be increased from '|| pre_sal

|| ' to '|| (emp_rec.sal));END LOOP;

END;

/


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Syntax for Creating a Function

A function is a named PL/SQL block that performs a task andreturns a value to the calling environment.

Syntax:

CREATE [ OR REPLACE ] FUNCTION function_name

[( argument [mode] data type, argument [mode] datatype )]

RETURN data type

ISLocal PL/SQL variable declarations

BEGIN

Define task performed by the function and return

result using RETURN statement

EXCEPTION

Handle exceptions if anyEND [ function_name];


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Functions in PL/SQL

Example 1

CREATE OR REPLACE FUNCTION cal_bonus

( p_eno emp.empno%TYPE )RETURN NUMBER

IS

v_sal emp.sal%TYPE;

BEGIN

SELECT sal INTO v_sal FROM emp

WHERE empno = p_eno;RETURN (v_sal * 0.1);

EXCEPTION

WHEN NO_DATA_FOUND THEN

RETURN -1;

END;


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Functions in PL/SQL

Example 2

CREATE OR REPLACE FUNCTION chk_dept

(p_deptno dept.deptno%TYPE) RETURNBOOLEAN

IS

v_deptno dept.deptno%type;

BEGIN

SELECT deptno into v_deptno FROM deptWHERE deptno = p_deptno;

RETURN TRUE;

EXCEPTION


RETURN FALSE;END;

/


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Calling Stored Functions from Different Locations

Functions can be called from different locations through SELECTand DML statements like:

Column list of SELECT command

WHERE and HAVING Clause

ORDER BY, GROUP BY Clauses

VALUES clause of INSERT command

SET clause of UPDATE command

Note: Not all functions can be called from above mentioned locations.

Rules for Calling a Function through a SQL


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Rules for Calling a Function through a SQLStatement

To be callable from SQL statement:

The function must be stored in database as either stand alonefunction or as a part of a package

The function can take only IN type of parameters

The formal parameters and return type of the function must beoracle data types

The function must not end the current transaction (commit orrollback) or rollback to a savepoint prior to the functionexecution

The function must not issue any alter session or alter systemcommands


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Difference between Procedures and Functions

Procedures Functions

Execute as a PL/SQL statement Invoked as part of an expression

Do not contain RETURN clause in theheader

Must contain a RETURN clause in theheader

Can return none, one or many valueswith the help of OUT & IN OUTparameters

Must return a value using the RETURNclause. Can also return one or manyvalues with the help of OUT and INOUT parameters.


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Referencing Objects from Other Schemas

To reference objects from other schemas we first need to haveappropriate privileges on the objects

To refer to objects in schemas other than our own, prefix theobject name with the schema name:

Schema_name.Object_name

Example: To get information from the emp table belonging toscott's schema the user HR should use the following command

SELECT * FROM scott.emp;

Note: The command will run successfully only if the user HR isgranted SELECT right on Scott's emp table

To execute a procedure belonging to scotts schema the user HR

will use the following commandEXECUTE scott.procedure_name


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Granting Privileges on Subprograms

The object privileges applicable to subprograms are

EXECUTE Grants right to execute the subprogram belonging to the schema of

the other user

Syntax

GRANT EXECUTE ON subprogram_name

TO username[, username.]|PUBLIC;

Example

GRANT EXECUTE ON emp_salary_increase TO PUBLIC;


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Revoking Privileges on Subprograms

To take back a privilege that is granted to a user

Syntax

REVOKE EXECUTE ON subprogram_name FROMUsername[,username..] |PUBLIC;

Example

REVOKE EXECUTE ON emp_salary_increase FROM

itp_jul_01, itp_jul_02;


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Dropping PROCEDURES and FUNCTIONS

To Delete a PROCEDURE:

DROP PROCEDURE ;e.g.

DROP PROCEDURE emp_salary_increase;

To Delete a FUNCTION:

DROP FUNCTION < Functionname >;

e.g.

DROP FUNCTION chk_dept;


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Local Procedures and Functions

The subprograms can also be defined within the declarativesection of a block. Such subprograms are known as LocalSubprograms

Local subprograms can also be defined within an anonymousblock

These subprograms follow the same scope and visibilityrules as any other PL/SQL identifier

It is only visible in the block in which it is declared

No other block can call local subprograms, as they are notvisible to any other block

Local Procedures and Functions within a Stored


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Local Procedures and Functions within a StoredSubprogram

CREATE OR REPLACE PROCEDURE emp_pro AS

CURSOR c_allEmp IS SELECT deptno, ename FROM emp;

v_dname dept.dname%TYPE;

-- Local function ,local to the procedure which will return thedept name for an employee

FUNCTION show_deptname (p_dno dept.deptno%TYPE) RETURN VARCHAR2IS

v_dname dept.dname%TYPE;

BEGIN

SELECT dname INTO v_dname FROM dept WHERE deptno=p_dno;

RETURN v_dname;

END show_deptname;

BEGIN

FOR v_rec IN c_allEmp LOOP

v_dname := show_deptname (v_rec.deptno);

DBMS_OUTPUT.PUT_LINE(v_rec.ename ||' belongs to

'||v_dname);END LOOP;

EXCEPTION


DBMS_OUTPUT.PUT_LINE('Wrong departmentnumber');

END emp_pro;

Difference between Stand Alone and Local


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Difference between Stand Alone and LocalSubprograms

Stand Alone Subprograms Local Subprograms

Stored Subprograms can be

called from any block submittedby a user that has EXECUTEprivilege on the subprogram

Local subprograms can be called

from only the block containingthe subprogram

The subprogram and the callingblock can be maintained

separately

The Subprogram and the callingblock are part of the same

program unit

Stand-Alone storedsubprograms cannot beoverloaded

Local subprograms can beoverloaded


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Methods of Passing Parameters

The various methods available for passing parameters tosubprograms are:

Positional

Pass actual parameters in the same order as formal parameters

Named

Pass actual parameters in arbitrary order by associating eachwith its corresponding formal parameter using special syntax

(=>) Combination

Pass at least the first actual parameters as positional and therest as named

Note: While using combination the positional parametersshould be passed first


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Methods of PassingParameters: Example

CREATE TABLE employee AS SELECT ename, sal, comm

FROMemp;TRUNCATE TABLE employee;

CREATE OR REPLACE PROCEDURE add_employee

(p_name IN emp.ename%TYPE DEFAULT 'unknown',

p_sal IN emp.sal%TYPE DEFAULT 1000,p_comm IN emp.comm%TYPE DEFAULT 0)

IS

BEGIN

INSERT INTO employee (ename,sal,comm)

VALUES( p_name, p_sal,p_comm);COMMIT;

END add_employee;

/


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Methods of PassingParameters: Example

BEGIN

add_employee ;

add_employee ('SMITH', 2000,600);

add_employee (p_sal=> 6000,p_comm=>200, p_name

=>'STEVE');

add_employee (p_sal =>4000) ;

add_employee('MARK',p_comm=>200, p_sal=> 6000);

END;

/

SELECT * FROM employee;

Note: All the positional parameters should precede the namedparameters in a subprogram call.


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Data Dictionary View

USER_SOURCE

Is used to obtain the text of a stored procedure or a storedfunction

USER_ERRORS Is used to find out the compilation errors in the subprogram,

currently getting compiled

One can use the SQL*Plus command SHOW ERRORS, insteadof firing a SELECT query on USER_ERRORS

USER_OBJECTS Is used to get the details of all the objects created in a

particular schema

USER_PROCEDURES

Is used to get the details of all procedures in that usersschema


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Summary

In this session, we have covered:

Need for subprograms

Creating Stored Procedures Invoking stored procedures from SQL*Plus and PL/SQL Block

Subprogram Parameter Modes IN, OUT and IN OUT

Creating Stored Functions

Calling Stored Functions from different locations

Privileges related to functions and procedures

Dropping procedures and functions

Local Procedures and Functions within a stored subprogram

Methods of passing Parameters

Data dictionary views related to subprograms

USER_OBJECTS USER_SOURCE

USER_PROCEDURES

USER_ERRORS


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Thank You

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Pls Ql 4 Sub Programs