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Creating Functions

Creating Functions

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Creating Functions

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  1. Creating Functions

  2. Objectives • After completing this lesson, you should be able to do the following: • Describe the uses of functions • Create client-side and server-side functions • Invoke a function • Remove a function • Differentiate between a procedure and a function

  3. Overview of Stored Functions • A function is a named PL/SQL block that returns a value. • A function can be stored in the database, as a database object, for repeated execution. • A function can be called as part of an expression.

  4. Syntax for Creating Functions CREATE [OR REPLACE] FUNCTION function_name (argument1 [mode1] datatype1, argument2 [mode2] datatype2, . . . RETURN datatype IS|AS PL/SQL Block;

  5. Oracle Procedure Builder Creating a Function Edit Textfile Systemeditor 1 Store in database Sourcecode 2 Compile p-code Execute

  6. Creating a Stored Function Using SQL*Plus • 1. Enter the text of the CREATE FUNCTION statement in a system editor or word processor and save it as a script file (.sql extension). • 2. From SQL*Plus, run the script file to compile the source code into p-code and store both in the database. 3. Invoke the function from an Oracle Server environment to determine whether it executes without error.

  7. Creating a Stored Function Using SQL*Plus: Example SQL> CREATE OR REPLACE FUNCTION get_sal 2 (v_id IN emp.empno%TYPE) 3 RETURN NUMBER 4 IS 5 v_salary emp.sal%TYPE :=0; 6 BEGIN 7 SELECT sal 8 INTO v_salary 9 FROM emp 10 WHERE empno = v_id; 11 RETURN (v_salary); 12 END get_sal; 13 /

  8. Creating a Function Using Procedure Builder Procedure Builder allows you to: • Create a client-side function • Create a server-side function • Drag and drop functions between client and server

  9. Executing Functions • Invoke a function as part of a PL/SQL expression. • Create a host variable to hold the returned value. • Execute the function. The host variable will be populated by the RETURN value.

  10. SQL> START get_salary.sql Procedure created. SQL> VARIABLE g_salary number SQL> EXECUTE :g_salary := get_sal(7934) PL/SQL procedure successfully completed. SQL> PRINT g_salary G_SALARY ------------------ 1300 Executing Functions in SQL*Plus: Example Calling environment GET_SAL function v_id 7934 RETURN v_salary

  11. Advantages of User-Defined Functions in SQL Expressions • Extend SQL where activities are too complex, too awkward, or unavailable with SQL • Query efficiency: functions used in the WHERE clause can filter data • Manipulate character strings • Provide parallel query execution

  12. Locations to Call User-Defined Functions • Select list of a SELECT command • Condition of the WHERE and HAVING clauses • CONNECT BY, START WITH, ORDER BY, and GROUP BY clauses • VALUES clauses of the INSERT command • SET clause of the UPDATE command

  13. Calling Functions from SQL Expressions: Restrictions • A user-defined function must be a stored function. • A user-defined function must be a ROW function, not a GROUP function. • A user-defined function only takes IN parameters, not OUT, or IN OUT. • Datatypes must be CHAR, DATE, or NUMBER, not PL/SQL types such as BOOLEAN, RECORD, or TABLE. • Return type must be an Oracle Server internal type.

  14. Calling Functions from SQL Expressions: Restrictions • INSERT, UPDATE, or DELETE commands are not allowed. • Calls to subprograms that break the above restriction are not allowed.

  15. Removing Functions • Using SQL*Plus: Drop a server-side function. • Using Procedure Builder: • Drop a server-side function. • Drop a client-side function.

  16. Removing a Server-SideFunction • Using SQL*Plus • Syntax • Example DROP FUNCTION function_name SQL> DROP FUNCTION get_salary; Function dropped.

  17. Function Procedure IN argument IN argument OUT argument IN OUT argument (DECLARE) BEGIN EXCEPTION END; (DECLARE) BEGIN EXCEPTION END; Procedure or Function? Calling Environment Calling Environment

  18. Comparing Procedures and Functions Procedure Execute as a PL/SQL statement No RETURN datatype Can return one or more values Function Invoke as part of an expression Must contain a RETURN datatype Must return a value

  19. Benefits of Stored Procedures and Functions • Improved performance • Improved maintenance • Improved data security and integrity

  20. Summary • A function is a named PL/SQL block that must return a value. • A function is invoked as part of an expression. • A stored function can be called in SQL statements.