Re: disallowing multiple NULLs in a unique constraint

Am Montag, 9. Februar 2004 06:06 schrieb David Garamond:
> SQL Server only allow one NULL in a unique constraint column (it's the
> unique index that does that, so the unique constraint behaves like that
> too). The question is, what is the best way to simulate that behaviour
> in Postgres? Can a CHECK constraint does that? Will a trigger with
> SELECT count(*) ... WHERE f IS NULL be too slow if the table is large?

You can time that yourself (but I suspect it won't be pretty), but I think 
that you're going to have all kinds of other problems if you base your 
database schema on the assumption that NULL = NULL.  Better fix the 
application.