Question

I’ve got the tables A and B. Table B has a foreign key constraint refering to table B. But since SQL Server 2000 only supports cascading delete, and not nullify, I decided to fix this with a trigger.

The problem: the trigger below doesn’t work:

CREATE TRIGGER dbo.TR_A_B_CascadingNullify ON dbo.A
FOR DELETE
AS
    UPDATE dbo.B
    SET idA = NULL
    WHERE idA IN (SELECT id FROM DELETED)
;

When deleting a row in A that isn’t refered to, everything works. But when a refered to row is deleted, it fails on the foreign key constraint with the message DELETE statement conflicted with COLUMN REFERENCE constraint 'FK_B_A'. The conflict occurred in database 'x', table 'B', column 'idA'.

And finally, when setting the option Enforce Foreign Key Constraint to No, the trigger does work, and the column in table B is set to NULL.

What am I doing wrong?

Answer 1

Your trigger fires after the DELETE, ie after all reference checks have been done. From the documentation of CREATE TRIGGER;

AFTER is the default when FOR is the only keyword specified.

Your only option afaik is to use an INSTEAD OF trigger.