I have this so far:

CREATE TRIGGER tgrExcessInventory on Production.ProductInventory FOR UPDATE AS IF EXISTS (SELECT 'True' FROM Inserted i JOIN Deleted d ON i.productID = d.ProductID AND i.locationID = d.LocationID WHERE (d.quantity + i.quantity) >= 800 OR i.quantity >=800 ) BEGIN RAISERROR('Cannot increase stock where units would be over 800 units',16,1) ROLLBACK TRAN END

1.) I just need help with modifying this trigger to execute its check code only if the Quantity column is updated.

***If additional information is needed, let me know exactly what so I can edit the question.

Thank you.