Hi all, can someone check my Trigger code... I never learn this stuff before... and I try to learn it...

Example,
Question: A student and his/her mentor cannot enrol in the same course (i.e. mentors and students they mentoring are not enrolled in the same course)

PHP Code:
CREATE OR REPLACE TRIGGER nevermentor
AFTER UPDATE OF STUDENT

DECLARE stdno STUDENT.STDNO%TYPE
       
BEGIN
SELECT S
.STDNO 
INTO stdno
FROM S STUDENT
WHERE S
.STDNO = :NEW.MENTOR;

IF NEW.
MENTOR =:S.STDNO 
AND S.COURSECODE  =:NEW.COURSE THEN
    raise_application_error
(-20012'Mentor and his/her student cannot enrol in the same course');

END IF;

END
And I attached together the table pix...