129-134 | High Performance Oracle Database Automation: Creating Oracle Applications with SQL and PL/SQL

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The Procedure Body

The SQL and PL/SQL statements that follow the BEGIN statement and precede the EXCEPTION and/or END statements is the body of the procedure. The highlighted portion of Listing 4.19 is the procedure s body.

Listing 4.19 The body of a procedure.

 PROCEDURE Calculate_GPA (iStudentSSN IN    number) IS   CURSOR StudentClasses_cur   IS   SELECT SC.course_number, C.course_hours   FROM   SCHEDULED_CLASSES SC,          CLASSES           C   WHERE  ssn = iStudentSSN   AND    credit_flag = 'Y'   AND    audit_flag  = 'N';   iTotalCredits    integer := 0;   iTotalHours      integer := 0;   FUNCTION Get_Course_Credits (iCourseID IN     integer)   RETURN integer   IS      iCreditsForClass integer := 0;   BEGIN     SELECT decode (course_grade, 'A', 4,                                  'B', 3,                                  'C', 2,                                  'D', 1, 0)     INTO   iCreditsForClass     FROM   SCHEDULED_CLASSES     WHERE  course_number = iCourseID     AND    ssn           = iStudentSSN;     RETURN iCreditsForClass;   END Get_Course_Credits; BEGIN   FOR StudentClasses_rec IN StudentClasses_cur LOOP     iCourse     := StudentClasses_rec.course_number;     iTotalHours := StudentClasses_rec.course_hours;     iTotalCredits :=   iTotalCredits                   + Get_Course_Credits (iCourse);     END LOOP;     UPDATE STUDENTS     SET    overall_gpa = (iTotalCredits / iTotalHours)     WHERE  ssn = iStudentSSN; EXCEPTION   WHEN ZERO_DIVIDE THEN       System.Log_Error (vObjectName =>'Calculate_GPA',                         vErrorText  => SQLERRM,                         vParameters => to_char (iCourseID)                                         '^'                                         to_char (iStudentSSN)); END Calculate_GPA;

Exception Handlers

Exception handlers are defined within the procedure to handle error conditions that could reasonably be expected to occur while the procedure is executing. In Listing 4.20, the developer feels that the ZERO_DIVIDE exception (one of the standard PL/SQL exceptions) could reasonably be expected to occur while calculating the student s new GPA.

Listing 4.20 The exception handler of a procedure.

 PROCEDURE Calculate_GPA (iStudentSSN IN    number) IS   CURSOR StudentClasses_cur   IS   SELECT SC.course_number, C.course_hours   FROM   SCHEDULED_CLASSES SC,          CLASSES           C   WHERE  ssn = iStudentSSN   AND    credit_flag = 'Y'   AND    audit_flag  = 'N';   iTotalCredits    integer := 0;   iTotalHours      integer := 0;   FUNCTION Get_Course_Credits (iCourseID IN     integer)   RETURN integer   IS      iCreditsForClass integer := 0;   BEGIN     SELECT decode (course_grade, 'A', 4,                                  'B', 3,                                  'C', 2,                                  'D', 1, 0)     INTO   iCreditsForClass     FROM   SCHEDULED_CLASSES     WHERE  course_number = iCourseID     AND    ssn           = iStudentSSN;     RETURN iCreditsForClass;   END Get_Course_Credits; BEGIN   FOR StudentClasses_rec IN StudentClasses_cur LOOP     iCourse     := StudentClasses_rec.course_number;     iTotalHours := StudentClasses_rec.course_hours;     iTotalCredits :=   iTotalCredits                   + Get_Course_Credits (iCourse);     END LOOP;     UPDATE STUDENTS     SET    overall_gpa = (iTotalCredits / iTotalHours)     WHERE  ssn = iStudentSSN; EXCEPTION   WHEN ZERO_DIVIDE THEN       System.Log_Error (vObjectName =>'Calculate_GPA',                         vErrorText  => SQLERRM,                         vParameters => to_char (iCourseID)                                         '^'                                         to_char (iStudentSSN)); END Calculate_GPA;

Exceptions occur for one of three reasons:

Oracle detects an unexpected error while the object is executing.

An exception is explicitly raised using the RAISE statement.

An exception is raised using the Raise_Application_Error() procedure.

Unexpected Errors

If an error occurs during the execution of an object, Oracle raises an exception and generates the most appropriate error text.

If the error message corresponds to one of the predefined exceptions that PL/SQL uses, the error can be handled using an exception handler for the predefined exception. Table 4.2 lists these predefined exceptions and their associated Oracle error message numbers .

**Table 4.2** Predefined exceptions in PL/SQL.

Exception	Associated Oracle Error
CURSOR_ALREADY_OPEN	ORA-06511
DUP_VAL_ON_INDEX	ORA-00001
INVALID_CURSOR	ORA-01001
INVALID_NUMBER	ORA-01722
LOGIN_DENIED	ORA-01017
NO_DATA_FOUND	ORA-01403
NOT_LOGGED_ON	ORA-01012
PROGRAM_ERROR	ORA-06501
STORAGE_ERROR	ORA-06500
TIMEOUT_ON_RESOURCE	ORA-00051
TOO_MANY_ROWS	ORA-01422
TRANSACTION_BACKED_OUT	ORA-00061
VALUE_ERROR	ORA-06502
ZERO_DIVIDE	ORA-01476

You can redeclare these predefined exceptions and create custom handlers for your new exceptions, but Oracle will not recognize your new exception when it attempts to raise one of the predefined exceptions. Your best bet is to leave the predefined exceptions alone and create your own user -defined exceptions.

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