Can an SQL constraint be used to prevent a particular value being changed when a condition holds?

Question

I know that SQL constraints can force data to meet validity criteria. However, what about criteria such as \"Student\'s grade can only be updated when the \'finalised\' flag

Answer 1

IMO, I'd say it should be done in either the application or the stored procedure (possibly both), rather than as an actual constraint (among other things, in your specific example, a grade being "finalized" doesn't always mean it's actually final).

However, if I were implementing this as a constraint, I'd use a CHECK constraint (again, using your example)

CONSTRAINT chk_grade CHECK(grade between 0 AND 100 and finalized = 0)

Check the specific syntax on that, but it's where I'd start.