Albe Laurenz <laurenz.albe@wien.gv.at> writes:
> Darren Duncan wrote:
>> I propose that this be generalized so that constraints may instead be nullary,
>> that is, range over zero or more attributes/columns instead.
> Since an imagined zero-column query would have an empty set of
> result columns, you could with equal force argue that these columns
> satisfy the condition or not, because the members of the empty
> set have all the properties you desire.
The semantics of a zero-column foreign key seem even less well
defined.
regards, tom lane
