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Oracle PL/SQL Functions Oracle Tips by Burleson

The most common use of functions is to hold both simple and complex mathematical equations that are performed frequently by an application, but other simple tasks can also be accomplished. Well-designed functions, like well-designed procedures, are coded to perform one task. Like procedures, functions can accept and return values to calling objects via parameters, but returning values from a function via parameters is typically viewed as a poor coding practice. Listing 1.10 presents a typical stored function.

Listing 1.10 A typical stored function.

FUNCTION Calculate_GPA (nSSN IN     integer)

RETURN NUMBER

IS
   nOverallGPA     number  := 0;
   iSumCredits     integer := 0;
   iTotalHours     integer := 0;
   iLogicStep      integer := 0;

BEGIN
   SELECT sum (credit_hours),
          sum (decode (course_grade,
                       'A', 4,
                       'B', 3,
                       'C', 2,
                       'D', 1, 0))
   INTO   iTotalHours,
          iSumCredits
   FROM   ENROLLED_COURSES
   WHERE  ssn = nSSN;

   iLogicStep := 1;
   nOverAllGPA := iSumCredits / iTotalHours;

   iLogicStep := 2;
   RETURN nOverAllGPA;

EXCEPTION
   WHEN OTHERS THEN
        SYSTEM_LOG.Log_Error (obj_name  => 'Calculate_GPA',
                              obj_step  => iLogicStep,
                              ora_error => substr (SQLERRM, 1, 65));
END Calculate_GPA;

This function closely resembles the procedural implementation of Calculate_GPA( ), but the function does have one advantage that the procedure doesn’t—the function can be called inside an SQL statement, as shown in Listing 1.11.

Listing 1.11 Use of the Calculate_GPA() function in an SQL statement.

UPDATE STUDENTS
SET    overall_gpa = Calculate_GPA (nSSN => ssn);

This is an excerpt from the book "High Performance Oracle Database Automation" by Jonathan Ingram and Donald K. Burleson, Series Editor.