On mån, 2010-10-25 at 17:57 -0700, Greg Stark wrote:
> Well if you lock multiple records then it's not clear what operations
> you should conflict with. Removing any one of them wouldn't actually
> invalidate the foreign key reference unless you remove the last one.
>
> I always assumed this was why we require the unique constraint at all.
I did mention that you would need an exclusion constraint in some of the
cases, to get an effect analogous to unique constraints.