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

From: vc <boston103_at_hotmail.com>
Date: 8 Dec 2005 08:49:27 -0800
Message-ID: <1134060567.603337.103190_at_g49g2000cwa.googlegroups.com>


Jon Heggland wrote:
> In article <1134052742.347560.142840_at_o13g2000cwo.googlegroups.com>,
> boston103_at_hotmail.com says...
> >
> > > I don't think a "regular" unknown/missing SQL NULL for a 2VL boolean
> > > domain should be regarded a truth value. That would be inconsistent with
> > > how NULL works in other domains.
> >
> > Then the logic ceases to be such if its truth values set include a
> > value for which the equality predicate evaluates to anything other than
> > TRUE or FALSE as I said elsewere.
>
> It does *not* include such a value. NULL is not a truth value any more
> than it is a number or a string.

I am missing something. If you store/use NULL as a logical value, haw can it *not* belong to the logical vaue domain with its logical operations? Sorry, but that does not make sense.

>
> > > I disagree. For consistency, I'd say that any boolean expression
> > > involving NULL booleans should evaluate to NULL, just like any
> > > arithmetic expression involving NULL integers evaluates to NULL (at
> > > least if you accept the excuse for how SUM() works:). I don't think it
> > > breaks logic more than it breaks arithmetic. If you disagree, can you
> > > give any examples of profound implications?
> >
> > See above. You cannot determine logical expression equivalence,
>
> Sure I can. If it is my truth tables you are worried about, they don't
> mention NULL, just TRUE and FALSE.

If your logical tables do not mention NULL, it means you never *use* it. Why do you want to store it, then ? It does not make any sense.

>
> > you
> > have no ability to derive anything in such 'logic', what use such
> > structure might have ?
>
> I see no more problems than NULLs cause in numeric computations.

The point that in such logic you cannot derive anything, or a good deal of expressions in such 'logic' cannot be judged equivalent does not strike you as odd ? The fact that even DeMorgan laws stop to work is also OK ?

> --
> Jon
Received on Thu Dec 08 2005 - 17:49:27 CET

Original text of this message