Follow us: Subscribe via RSS Feed Connect on YouTube Connect on YouTube

Pages

Thursday, 7 April 2016

Procedures and Functions

Subprograms in PL/SQL

PL/SQL blocks are anonymous, cannot be called from other PL/SQL blocks
Subprogram is a named PL/SQL block that could be either
Procedure, or
Function, or
Package

Syntax for Creating a Procedure

     Stored Procedure
 A stored procedure is a named PL/SQL block that performs an action. It can be stored in the database as a database object for repeated execution.

CREATE  [ OR REPLACE ] PROCEDURE  proc_name[(argument   [mode]   data type, argument   [mode]  data type,……)]
-- PROCEDURES and FUNCTIONS may or may not accept arguments
IS
       Local PL/SQL variable declarations
BEGIN
       Define action performed by the procedure
EXCEPTION
       Handle exceptions, if any
END [ proc_name];

Advantage of Replace option

This option replaces the previous definition of the FUNCTION, PROCEDURE, PACKAGE in the schema with the same name. The advantage of using the “REPLACE” option over “Dropping and recreating an object with new definition” is that the object privileges granted on the object get automatically revoked when you drop the object and are to be explicitly granted again when you recreate it with the new definition where as when the REPLACE option is used the object privileges remain unchanged.
Proc_name    : Name of the procedure
Argument      : Name of the PL/SQL variable whose value is passed to, populated by the  calling environment or both , depending on the mode being used.
Mode            : Mode of the argument IN , OUT or IN OUT (explained later)
Datatype       : Datatype of the argument

The REPLACE option indicates that if the procedure exist it’s definition will be overwritten by a new procedure body.

Eg # 1

CREATE OR REPLACE PROCEDURE raise_salary (p_eno emp.empno%TYPE)
IS
BEGIN
   UPDATE emp
      SET sal = sal * 0.1
    WHERE empno = p_eno;
END raise_salary;

RAISE_APPLICATION_ERROR Procedure

This procedure is used to display error messages along with error numbers
Example
          RAISE_APPLICATION_ERROR(-20001, ‘Invalid Employee’);

Note:
When called, RAISE_APPLICATION_ERROR ends a subprogram, rolls back any database changes it made, and returns a user-defined error message to the application
Error numbers should be between -20000 and -20999

Parameters Modes in Procedures and Functions

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



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 < 2000
   THEN
      UPDATE emp
         SET sal = sal + vsal * 0.1
       WHERE empno = p_eno;
   END IF;
-- An exception handler to raise error if empno is not valid
EXCEPTION
   WHEN NO_DATA_FOUND
   THEN
      DBMS_OUTPUT.put_line('Empno does not exist');
ENDraise_salary;

Invoking a Procedure

There are two methods to Invoke a Procedure
Invoke a Procedure from another PL/SQL block
  Example:
          BEGIN
                   raise_salary(1002);
          END;

Invoke a procedure from SQL*Plus environment by using EXECUTE command
Example
-- 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;
EXCEPTION
   WHEN NO_DATA_FOUND
   THEN
      raise_application_error (-20001, 'Employee does not exist');
END query_emp;

Note: In this example, p_eno parameter value cannot be changed, since it is defined as IN parameter. It receives a value from the calling environment. Parameters p_name and p_sal do not receive any value from the calling environment. The procedure query_emp assigns value to the two parameters and these values are passed back to the calling environment.

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 in the EXECUTE syntax

IN OUT Parameter: Example

CREATE OR REPLACE PROCEDURE emp_salary_increase (
   p_emp_id   IN       emp.empno%TYPE,
   p_salary   IN OUT   emp.sal%TYPE
)
IS
BEGIN
   IF p_salary BETWEEN 1000 AND 2000
   THEN
      p_salary := p_salary * 1.2;
   ELSIF p_salary BETWEEN 2000 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
   THEN
      DBMS_OUTPUT.put_line(SQLERRM);
END;
/

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 INupdated_sal
   LOOP
      pre_sal := emp_rec.sal;
      emp_salary_increase (emp_rec.empno, emp_rec.sal);
      DBMS_OUTPUT.put_line(   ' The salary of '
                            || emp_rec.empno
                            || ' will be increased from '
                            || emp_rec.sal
                            || '  to  '
                            || (emp_rec.sal + pre_sal)
                           );
   END LOOP;
END;
/

Syntax for Creating a Function

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

Syntax:
CREATE  [ OR REPLACE ] FUNCTION  function_name
[( argument   [mode]   data type, argument   [mode]  data type )]
RETURN  data type
IS
       Local PL/SQL variable declarations
BEGIN
     Define task performed by the function and return
     result using   RETURN statement
EXCEPTION
       Handle exceptions if any
END [ function_name];



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;

Example 2
        
CREATE OR REPLACE FUNCTION chk_dept (p_deptno dept.deptno%TYPE)
   RETURN BOOLEAN
IS
   v_deptno   dept.deptno%TYPE;
BEGIN
   SELECT deptno
     INTO v_deptno
     FROM dept
    WHERE deptno = p_deptno;

   RETURN TRUE;
EXCEPTION
   WHEN NO_DATA_FOUND
   THEN
      RETURN FALSE;
END;

Calling Stored Functions from Different Locations

Functions can be called from different locations through SELECT and 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 Statement

To be callable from SQL statement:
The function must be stored in database as either stand alone function 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 be oracle data types
The function must not end the current transaction (commit or rollback) or rollback to a savepoint prior to the function execution
The function must not issue any alter session or alter system commands

Difference between Procedures and Functions

 


Referencing Objects from Other Schemas

To reference objects from other schemas we first need to have appropriate privileges on the objects
To refer to objects in schemas other than our own, prefix the schema name with the object name:
                   Schema_name.Object_name
Example: To get information from the emp table belonging to scott'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 is granted SELECT right on Scott's emp table

To execute a procedure belonging to scott’s schema the user HR will use the following command
          EXECUTE scott.procedure_name

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;

DEBUG
Grants right to debug the subprogram belonging to the schema of the other user
Syntax
          GRANT DEBUG ON subprogram_name TO username[, username….]|PUBLIC;
Example
  GRANT DEBUG ON emp_salary_increase TO PUBLIC

Revoking Privileges on Subprograms

To take back a privilege that is granted to a user
Syntax
   REVOKE EXECUTE/DEBUG ON subprogram_name FROM
   Username[,username…..] |PUBLIC;

Example
   REVOKE  EXECUTE ON emp_salary_increase FROM itp_jul_01, itp_jul_02;

Dropping PROCEDURES and FUNCTIONS
To Delete a PROCEDURE:

DROP PROCEDURE <Procedurename>;
e.g.
DROP PROCEDURE emp_salary_increase;

To Delete a FUNCTION:

 DROP FUNCTION < Functionname >;
 e.g.
 DROP FUNCTION  chk_dept;
Local Procedures and Functions
The subprograms can also be defined within the declarative section of a block, such subprograms are known as Local Subprograms

Local subprograms can also be defined within an anonymous block

These subprograms follow the same scope and visibility rules 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 not visible to any other block
Local Procedures and Functions within a Stored Subprogram

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 the dept name for an employee
   FUNCTION show_deptname (p_dno dept.deptno%TYPE)
      RETURN VARCHAR2
   IS
      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
   WHEN NO_DATA_FOUND
   THEN
      DBMS_OUTPUT.put_line
                          ('Wrong department                          number');
END emp_pro;


Difference between Stand Alone and Local Subprograms



Methods of Passing Parameters

 The various methods available for passing parameters to subprograms are:

Positional
          Pass actual parameters in the same order as formal parameters
Named
          Pass actual parameters in arbitrary order by associating each with its corresponding formal parameter using special syntax (=>)
Combination
          Pass some of the actual parameters as positional and some as named

  Note: While using combination the positional parameters   should be passed first

Methods of Passing Parameters: Example

CREATE TABLE employee AS SELECT ename, sal, comm
                                                              FROM emp;
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;
ENDadd_employee;
/

Methods of Passing Parameters: 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_sal=> 6000,p_comm=>200); 
END;
/
SELECT * FROM employee;
          
Note: All the positional parameters should precede the named parameters in a subprogram call.

Data Dictionary View

USER_SOURCE
Is used to obtain the text of a stored procedure or a stored function

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, instead of 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 user’s schema


Share this article :

0 comments:

Post a Comment