Question

I am implementing exclusive arc pattern of resolving multiple parents for a given table. I wrote the below table level check constraint for use in SQL Server 2008. The proble with this, if there are 3 columns, the query grows so much bigger. Is there any better to do it?

check( 
(Parent1Id is null AND Parent2Id is not null) 
OR  (Parent1Id is not null AND Parent2Id is null))

Answer 1

How about check(COALESCE(Parent1ID, Parent2ID) IS NOT NULL) – this makes sure at least one is set, but to do the negative check I can’t think of a quick solution.

Come to think of it, how about: (warning – not much shorter)

check(
CASE WHEN Parent1ID IS NULL THEN 0 ELSE 1 END
+ CASE WHEN Parent2ID IS NULL THEN 0 ELSE 1 END
+ CASE WHEN Parent3ID IS NULL THEN 0 ELSE 1 END
+ CASE WHEN Parent4ID IS NULL THEN 0 ELSE 1 END
= 1
)