Add unique constraint based on field value

Question

For the following table:

I\'d like to add a constraint that if IsBanned fl

Answer 1

Actually, you can not define conditional structures in DDL syntax. Your field can be either NULL or NOT NULL - there's no third option (and it cannot depend of another field in structure)

But you can still emulate desired behavior via triggers. You can interrupt UPDATE/INSERT statement if incoming data is invalid in terms of your logic. That can be done via:

CREATE TRIGGER `bannedOnCheck`
BEFORE INSERT ON `fa_ranking_system`.`Player`
FOR EACH ROW
BEGIN
  IF(new.IsBanned && new.BannedOn IS NULL) THEN
    SIGNAL 'Integrity check failed: can not set banned without ban date'
  END IF
END