Re: Does Codd's view of a relational database differ from that ofDate& Darwin? [M.Gittens]
From: Paul <paul_at_test.com>
Date: Tue, 07 Jun 2005 16:53:13 +0100
Message-ID: <42a5c2e9$0$41899$ed2619ec_at_ptn-nntp-reader03.plus.net>
Date: Tue, 07 Jun 2005 16:53:13 +0100
Message-ID: <42a5c2e9$0$41899$ed2619ec_at_ptn-nntp-reader03.plus.net>
Alexandr Savinov wrote:
> To say "if NULL means unknown" is the same as to say "if 0 is equal 1"
> or "if empty set is full set". Unknown and null are two different things
> and deserve to have to special designations.
>
> NULL means absence
> UNKNOWN means presence with unknown identity