use triggers to enforce interigity

Hi,
My homework assignment is to use triggers to enforce integrity. I have student(student_id, student_name), course(course_id,course_title), and studentCourse(student_id, course_id) tables. each table has a trigger. in the trigger of student table, when the student_id is updated, the same student_id in studentCourse is updated too. the trigger in studentCourse check if new student_id that will be set in the studentCourse has exist in the student table. if not, the trigger will be raise a error and give up the updating.
But when I update the student_id of student table, I got error. I guess I should not use my approach to enforce integrity. How to enforce them?

Thank a lot,

Jingyan Xu Received on Sun Nov 28 1999 - 18:33:32 CST