Re: No exceptions?

From: Marshall <>
Date: 1 Jul 2006 11:13:28 -0700
Message-ID: <>

J M Davitt wrote:
> I think I got it. Am I correct in understanding that JH said,
> "If an empty candidate key is declared, any other keys are
> superkeys?"

In fact we can go further: if an empty key exists, then *all* sets of attributes are superkeys.

A superkey is a set of attributes some subset of which is a candidate key.

The empty set is a subset of every set.

Marshall Received on Sat Jul 01 2006 - 20:13:28 CEST

Original text of this message