mysql - How do I enforce uniqueness in a table?

Question

For example, I have to program an enrolment table which has:

1. enrolment_id
2. academic_period
3. results
4. student_id
5. subject

I want to enforce to make sure that a student can't enroll in a subject more than once in a specific academic period. So, the constraint shall involve student_id, subject, and academic period columns.

I'm still unsure how do I make this happen. Any help?

Answer 1

Add a unique constraint to your table:

ALTER TABLE yourtable ADD CONSTRAINT constraintname UNIQUE (student_id, subject, academic_period)