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
Creating Functions
Invoke a function
Remove a function
Differentiate between a procedure and a function
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
schema object, for repeated execution.
Syntax for Creating Functions
CREATE [OR REPLACE] FUNCTION function_name
[(parameter1 [mode1] datatype1,
parameter2 [mode2] datatype2,
. . .)]
RETURN datatype
IS|AS
PL/SQL Block;
A function can be called as part of an expression.
The PL/SQL block must have at least one RETURN
statement.
Creating a Function
Oracle
Procedure
Builder
1
Editor
Code
Save
SQL*Plus
2
Creating a Stored Function
by Using SQL*Plus
Code
SQL> START file.sql
1. Enter the text of the CREATE FUNCTION statement
in an editor.
2. Run the script file to store the source code and
compile the function.
3. Use SHOW ERRORS to see compilation errors.
Oracle
Source code
Compile
4. When successfully compiled, the function is ready
for execution.
P code
Execute
<Course name> <Lesson number>-
Creating a Stored Function by Using
SQL*Plus: Example
SQL>
2
3
4
5
6
7
8
9
10
11
12
13
Invoke a function as part of a PL/SQL expression.
CREATE OR REPLACE FUNCTION get_sal
(v_id IN
emp.empno%TYPE)
RETURN NUMBER
IS
v_salary
emp.sal%TYPE :=0;
BEGIN
SELECT sal
INTO
v_salary
FROM
emp
WHERE empno = v_id;
RETURN v_salary;
END get_sal;
/
Create a host variable to hold the returned value.
Execute the function. The host variable will be
populated by the RETURN value.
Executing Functions in SQL*Plus:
Example
Calling environment
GET_SAL function
v_id
7934
Executing Functions
RETURN v_salary
Creating a Function by 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
SQL> START get_salary.sql
Function 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
Creating Functions by Using
Procedure Builder: Example
Return the tax based on a specified value.
FUNCTION tax
(v_value IN NUMBER)
RETURN NUMBER
IS
BEGIN
RETURN (v_value * .08);
END tax;
Executing Functions in
Procedure Builder: Example
Calling environment
TAX function
v_value
1000
RETURN (computed value)
Display the tax based on a specified value.
PL/SQL> .CREATE NUMBER x PRECISION 4
PL/SQL> :x := tax(1000);
PL/SQL> TEXT_IO.PUT_LINE (TO_CHAR(:x));
80
<Course name> <Lesson number>-
Advantages of User-Defined Functions in
SQL Expressions
Extend SQL where activities are too complex, too
awkward, or unavailable with SQL
Can increase efficiency, by using them in the
WHERE clause to filter data, as opposed to
filtering the data in the application
Can manipulate character strings
Locations to Call User-Defined Functions
Invoking Functions in SQL Expressions:
Example
SQL> CREATE OR REPLACE FUNCTION tax
2
(v_value IN NUMBER)
3
RETURN NUMBER
4 IS
5 BEGIN
6
RETURN (v_value * .08);
7 END tax;
8 /
Function created.
SQL> SELECT empno, ename, sal, tax(sal)
2 FROM emp;
Calling Functions from SQL Expressions:
Restrictions
A user-defined function must be a stored function.
Select list of a SELECT command
Condition of the WHERE and HAVING clauses
A user-defined function must be a SINGLE-ROW
function, not a GROUP function.
CONNECT BY, START WITH, ORDER BY, and
GROUP BY clauses
A user-defined function only takes IN parameters,
not OUT or IN OUT.
VALUES clauses of the INSERT command
Data types must be valid SQL datatypes, CHAR,
DATE, or NUMBER.
SET clause of the UPDATE command
Data types cannot be PL/SQL types such as
BOOLEAN, RECORD, or TABLE.
Calling Functions from SQL Expressions:
Restrictions
Removing Functions
INSERT, UPDATE, or DELETE commands are not
allowed.
Using SQL*Plus:
Calls to subprograms that break the above
restriction are not allowed.
Using Procedure Builder:
Drop a server-side function
Drop a server-side function
Delete a client-side function
<Course name> <Lesson number>-
Removing Server-Side
Functions
Removing a Server-Side
Function
Using Procedure Builder:
Using SQL*Plus:
1. Connect to the database.
2. Expand the Database Objects node.
Syntax
3. Expand the schema of the owner of the function.
DROP FUNCTION function_name
4. Expand the Stored Program Units node.
5. Click the function that you want to drop.
Example
6. Click Delete in the Object Navigator.
SQL> DROP FUNCTION get_sal;
Function dropped.
7. Click Yes to confirm.
Removing a Client-Side
Function
Procedure or Function?
Function
Procedure
Using Procedure Builder:
Calling
Environment
1. Expand the Program Units node.
IN parameter
OUT parameter
Calling
Environment
IN parameter
2. Click the function that you want to remove.
IN OUT parameter
3. Click Delete in the Object Navigator.
(DECLARE)
(DECLARE)
4. Click Yes to confirm.
BEGIN
BEGIN
EXCEPTION
EXCEPTION
END;
END;
Comparing Procedures
and Functions
Procedure
Function
Execute as a PL/SQL
statement
Invoke as part of an
expression
No RETURN data type
Must contain a RETURN
data type
Can return none, one or
many values
Must return a single value
<Course name> <Lesson number>-
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