Oracle FAQ Your Portal to the Oracle Knowledge Grid
HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US
 

Home -> Community -> Usenet -> comp.databases.theory -> Re: No exceptions?

Re: No exceptions?

From: Marshall <marshall.spight_at_gmail.com>
Date: 1 Jul 2006 11:13:28 -0700
Message-ID: <1151777608.325833.296770@m73g2000cwd.googlegroups.com>


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 - 13:13:28 CDT

Original text of this message

HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US