Question

I am trying to add a check constraint which verity if after an update the new value (which was inserted) is greater than old values which is already stored in table.

For example i have a “price” column which already stores value 100, if the update comes with 101 the is ok, if 99 comes then my constraint should reject the update process. Can this behavior be achieved using check constraints or should i try to use triggers or functions ?

Please advice me regarding this…

Thanks,
Mircea

Answer 1

Check constraints can’t access the previous value of the column. You would need to use a trigger for this.

An example of such a trigger would be

CREATE TRIGGER DisallowPriceDecrease
ON Products
AFTER UPDATE
AS
IF NOT UPDATE(price) 
   RETURN

IF EXISTS(SELECT * FROM inserted i 
                     JOIN deleted d 
                     ON i.primarykey = d.primarykey 
                      AND i.price< d.price)
BEGIN
    ROLLBACK TRANSACTION
    RAISERROR('Prices may not be decreased', 16, 1)
END