On 24-4-2012 10:18, Thomas Steinmaurer wrote: >> 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.
Even it is compound, the NULLs are not taken into account for uniqueness, only the non-null parts: http://www.firebirdsql.org/manual/nullguide-keys.html -- Mark Rotteveel
