Question

I am working on triggers in sql. I am trying to do an update trigger, however I want it to work only if a certain condition is met.

For example lets say I have a table X and two columns A,B.
I want to be able to update A or B only when A is less than B for the new values to be updates.

So I am doing a trigger like this

create trigger utrigger
on X
for update as
if (update(A) OR update(B))
begin


 if (A>B)
 RAISERROR (N' Incorrect %s %d.', -- Message text.
       10, -- Severity,
       1, -- State,
       N'number', -- First argument.
       5); -- Second argument.

end

However I think I am doing it wrong. Whats wrong in this?

Answer 1

You need to use the INSERTED virtual table.

create trigger utrigger
on X
for update as
if (update(A) OR update(B))
begin
 if exists (SELECT *   -- this subquery breaches the condition
            FROM INSERTED
            WHERE A>=B)    -- might need some isnull if nulls are not allowed
 RAISERROR (N' Incorrect %s %d.', -- Message text.
       10, -- Severity,
       1, -- State,
       N'number', -- First argument.
       5); -- Second argument.
end