Re: So what's null then if it's not nothing?

Gene Wirchenko wrote:

> On 25 Nov 2005 01:49:04 -0800, michael_at_preece.net wrote:
>
> [snip]
>
> >something. We can know something is empty. We can't know anything about
> >something that doesn't exist. We have no facts about it. We have no
> >data.
>
> We can know that it does not exist.
>
> Sincerely,
>
> Gene Wirchenko

If what does not exist? You think we should have some special value to represent the "fact" that something doesn't exist? Go on then - be fair about it... Please choose a small file in your database. Now please list all of the things it doesn't know anything about. I could, if challenged, tell you exactly which things are empty, or NULL, in any of the files here - if I was allowed to.

Really there are two reasons for NULL as we now know it. One of them is perfectly acceptable in any context, the other a mere excuse for a deficiency in a model.

NULL, as defined in mathematics and according to the root meaning for the word in the dictionary, is, properly, an empty set or "not any". That is the perfectly acceptable reason for NULL. There is no 3VL with this NULL. There is no distinction between two NULL values. Things are either distinct or not distinct - never unknown.

The mere excuse for the deficiency in a model, is when it's used as a "placeholder" because the model insists that every "row" must have the same number of "columns" - even though that might not be true in the real world. This is inappropriate, misleading and the source of great confusion. If you (SQL) need a special value for this then use something else - use "UNKNOWN" or whatever you like, but don't corrupt NULL. Mike. Received on Tue Nov 29 2005 - 02:46:15 CET