More trigger hints

Here is a bit of code to get you started for the assignment:

CREATE OR REPLACE TRIGGER CourseRegistration
INSTEAD OF INSERT ON Registrations
REFERENCING NEW AS new
FOR EACH ROW
DECLARE
hasPassed Int;
BEGIN
   SELECT COUNT (*) INTO hasPassed FROM PassedCourses 
     WHERE course  = :new.course AND student = :new.student;
   IF hasPassed > 0 THEN 
     RAISE_APPLICATION_ERROR(-20001,'Student has already passed');
   ELSE
     RAISE_APPLICATION_ERROR(-20002,'Student has not passed the course! This error is just a placeholder.');
   END IF;
END;
/