Question

I have two tables:

info: ID, fee_id

and

fee: ID, amount

and a reference between them (SQL Server 2008):

ALTER TABLE info WITH CHECK ADD CONSTRAINT FK_info_fee FOREIGN KEY(fee_id)
REFERENCES fee (ID)
ALTER TABLE info CHECK CONSTRAINT FK_info_fee
GO

How to configure this reference that way so a record in fee will be deleted if info.fee_id becomes NULL

EDIT: or maybe set info.fee_id to NULL on deleting the corresponding record in fee.

Anyway I can do it this way:

UPDATE info SET fee = NULL WHERE = ..
DELETE FROM fee WHERE ..

but I’m sure that this can be done by the database itself.

Answer 1

Some thoughts:

• If you have a one:one reference then can the 2 tables be combined?
• Drilling up from child to parent is odd: if it’s 1:1 then can you reverse the FK direction and simply CASCADE NULL?
• Otherwise, you’ll have to use a trigger but assuming 1:1 makes me uneasy…
• … unless you have a unique constraint/index on info_fee.fee_id

Like so:

ALTER TABLE info WITH CHECK ADD
CONSTRAINT FK_fee_info_fee FOREIGN KEY (id) REFERENCES info_fee (fee_ID) ON DELETE SET NULL