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