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

From: Jon Heggland <>
Date: Tue, 29 Nov 2005 16:18:43 +0100
Message-ID: <>

In article <>, says...
> Jon Heggland wrote:
> [...]
> > SQL is confused, and breeds confusion. For one thing, NULL is not a
> > value. If it were, it would be equal to itself.
> With respect to nulls, SQL is no more confused that Codd's original
> work on which SQL's null treatment is based. There is no need to
> attack SQL whose deficiencies are well known if all one wants to
> discuss is the notion of null..

Then consider my statement an attack on Codd, if SQL is faithful to his work. Alternatively, tell me how SQL is deficient with respect to Codd.

> > > Whether or not two values are considered distinct is irrelevant to the
> > > null = null comparison.
> >
> > By SQL fiat, perhaps. But *should* it be? What gives SQL the right to
> > redefine notions of equality and "distinctness" in this manner? Or never
> > mind the right; does it make *sense*? Is it worth the price?
> null=null evaluates to unknown according to the 3vl logic rules.

Indeed? Is NULL an inherent part of 3VL? Reference? I don't think Codd invented 3VL ...

> Again, SQL per se does not have much to do with the notion of null.
> Please see Codd's article I mentioned earlier and comment on it rather
> that criticizing SQL.

Isn't it pretty much the same? Again, please tell me what you consider the deficiencies of SQL.

As for Codd's article, I think it is a bad idea in itself to use 3VL. Codd himself admits it produces seemingly paradoxical results and breaks what we expect to be tautologies. Also, to conflate the unknown truth value with null seems like a huge blunder. Finally, he discusses the RM's relationship to predicate logic, but fails completely to consider the effects of nulls on this relationship.

Received on Tue Nov 29 2005 - 16:18:43 CET

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