Enforce constraint checking only when inserting rows in MSSQL?

Question

Is there a way to enforce constraint checking in MSSQL only when inserting new rows? I.e. allow the constraints to be violated when removing/updating rows?

Update: I mean FK constraint.

Answer 1

I think your best bet is to remove the explicit constraint and add a cursor for inserts, so you can perform your checking there and raise an error if the constraint is violated.

Answer 2

You could create an INSERT TRIGGER that checks that the conditions are met. That way all updates will go straight through.

CREATE TRIGGER employee_insupd
ON employee
FOR INSERT
AS
/* Get the range of level for this job type from the jobs table. */
DECLARE @min_lvl tinyint,
   @max_lvl tinyint,
   @emp_lvl tinyint,
   @job_id smallint
SELECT @min_lvl = min_lvl, 
   @max_lvl = max_lvl, 
   @emp_lvl = i.job_lvl,
   @job_id = i.job_id
FROM employee e INNER JOIN inserted i ON e.emp_id = i.emp_id 
   JOIN jobs j ON j.job_id = i.job_id
IF (@job_id = 1) and (@emp_lvl <> 10) 
BEGIN
   RAISERROR ('Job id 1 expects the default level of 10.', 16, 1)
   ROLLBACK TRANSACTION
END
ELSE
IF NOT (@emp_lvl BETWEEN @min_lvl AND @max_lvl)
BEGIN
   RAISERROR ('The level for job_id:%d should be between %d and %d.',
      16, 1, @job_id, @min_lvl, @max_lvl)
   ROLLBACK TRANSACTION
END

Answer 3

What sort of constraints? I'm guessing foreign key constraints, since you imply that deleting a row might violate the constraint. If that's the case, it seems like you don't really need a constraint per se, since you're not concerned with referential integrity.

Without knowing more about your specific situation, I would echo the intent of the other posters, which seems to be "enforce the insert requirements in your data access layer". However, I'd quibble with their implementations. A trigger seems like overkill and any competent DBA should sternly rap you on the knuckles with a wooden ruler for trying to use a cursor to perform a simple insert. A stored procedure should suffice.