> Den 2012-04-24 10:18 skrev Thomas Steinmaurer såhär: >> >>> Is there any way to enforce uniqueness of all non-nulls in a nullable >>> column? >> >>> The "business requirement" would be "this kind of thing has an optional >>> attribute, that, if it exists, is unique". For example, a company may or >>> may not exist in the Byro van Dijk company database, but if it does >>> exist it will have a unique BvD id. I'd like to enforce this uniqueness. >> >> I'm sure I don't understand the question properly, because a Firebid >> UNIQUE constraint on a null-able column doesn't take NULLs into account, >> as long as it isn't a compound UNIQUE constraint made up from> 1 >> columns.. >> >> >> > > Oh!? I didn't know. RTFM then... :-) I was working in SQL Server and > then this cropped up.
Yeah, welcome in the world writing applications supporting multiple backends. Little, neat differences along different products. ;-) Regards, Thomas > It didn't cross my mind that it could be > different... SQL Server UNIQUE allows only a single null. I really think > this should be optional, e.g. like this: > 1. constraint X unique (Y) ignore null > 2. constraint X unique (Y) restrict null > > 1 would be like FB, 2 like SQL Server.
