On 12 May 2010 07:34, Mike Christensen <m...@kitchenpc.com> wrote: > I have the following constraint which almost works: > > ALTER TABLE ingredientforms ADD CONSTRAINT > ingredientforms_UniqueIngredientForm UNIQUE(IngredientId, > FormDisplayName); > > However, I want to allow rows that have the same IngredientId > FormDisplayName /iff/ FormDisplayName is null. If FormDisplayName is > not null, then it must be unique. > > 1, NULL > 1, NULL > > Would be allowed. > > 1, 'Foo' > 1, 'Foo' > > would violate the constraint. > > 1, 'Foo' > 1, 'Bar' > > would be allowed. > > Any way to do this? Insert performance is not an issue since the > table is almost never changed.. > > Mike > > > What you've said you want to do looks like what you'd be allowed to do anyway. You're allowed duplicate values on a unique constraint if one of the columns is null.
Regards Thom
