Oracle/PLSQL: Creating Functions

In Oracle, you can create your own functions.

The syntax for a function is:

CREATE [OR REPLACE] FUNCTION function_name
    [ (parameter [,parameter]) ]
    RETURN return_datatype
IS | AS
    [declaration_section]
BEGIN
    executable_section
[EXCEPTION
    exception_section]
END [function_name];

When you create a procedure or function, you may define parameters. There are three types of parameters that can be declared:

1. IN - The parameter can be referenced by the procedure or function. The value of the parameter can not be overwritten by the procedure or function.
2. OUT - The parameter can not be referenced by the procedure or function, but the value of the parameter can be overwritten by the procedure or function.
3. IN OUT - The parameter can be referenced by the procedure or function and the value of the parameter can be overwritten by the procedure or function.

The following is a simple example of a function:

CREATE OR REPLACE Function FindCourse
   ( name_in IN varchar2 )
   RETURN number
IS
    cnumber number;

    cursor c1 is
    select course_number
      from courses_tbl
      where course_name = name_in;

BEGIN

open c1;
fetch c1 into cnumber;

if c1%notfound then
     cnumber := 9999;
end if;

close c1;

RETURN cnumber;

EXCEPTION
WHEN OTHERS THEN
      raise_application_error(-20001,'An error was encountered - '||SQLCODE||' -ERROR- '||SQLERRM);
END;

This function is called FindCourse. It has one parameter called name_in and it returns a number. The function will return the course number if it finds a match based on course name. Otherwise, it returns a 99999.

You could then reference your new function in an SQL statement as follows:

select course_name, FindCourse(course_name) as course_id
from courses
where subject = 'Mathematics';