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@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

I don't think NULL should mean absence.

As an example, consider storing middle names. Some people don't have middle names. But I think it would be good practice to store an empty string for people without middle names, and reserve NULLs for people whose middle name is unknown, whether or not it exists.

So NULL means unknown, irrespective of whether it's present or absent.

This is presupposing you want to have NULLs in the first place, which is another question altogether.

Paul. Received on Tue Jun 07 2005 - 10:53:13 CDT