Description of the illustration adfns062.eps

This figure shows an exception and an associated exception handler. A trigger uses a conditional statement that checks for an error condition and raises an application error. The user-defined error code and message are returned to the error handler.

PROCEDURE fire_emp (empid NUMBER) IS
  invalid_empid EXCEPTION
  PRAGMA EXCEPTION_INIT (invalid_empid, -20101);
BEGIN
  DELETE FROM emp WHERE empno = empid;
EXCEPTION
  WHEN invlid_empid THEN
   INSERT INTO emp_audit
    VALUES (empid, 'Fired before probation ended');
END;

This program returns the error number 20101 to the invoking environment (the preceding program).

TRIGGER emp_probation
BEFORE DELETE ON emp
FOR EACH ROW
BEGIN
  IF (sysdate - :old.hiredate) < 30 THEN
    raise_application_error(20101,
     'Employee' || old.ename || ' on probation')
  END IF;
END;