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

From: <michael_at_preece.net>
Date: 24 Nov 2005 17:34:45 -0800
Message-ID: <1132882485.862127.147590@g14g2000cwa.googlegroups.com>


David Cressey wrote:

> <michael_at_preece.net> wrote in message
> news:1132790275.193031.254020_at_g49g2000cwa.googlegroups.com...
>
>
> > > The only thing that NULL means is "there's no value here". Period. I'm
> > > sorry if that doesn't make sense to you - but that's just the way it is.
> >
> > That makes perfect sense to me. What's more - I'm in total 100%
> > agreement. The confusion only arises when it is interpreted to mean the
> > value is absent. Can you see the difference that exists between
> > something being present and yet having no value and something being
> > absent? That's the whole reason for NULL - to represent something being
> > present and yet having no value.
> >
> > >
> > > > Absence is the problem word. If I want something to be
> > > >absent I'll delete it from the database.
>
> If I'm reading the aobve right, the whole debate stems from a choice in
> terminology:
>
> To you, "There's no value here" makes sense. But "there is an absence of a
> value here" is confusing.
>
> To me, they mean the same thing. Are we close to wrapping this topic up?

We're close to a shared understanding. You understand the distinction I make. I would like to continue the discussion at least to the point where you, and others, also see the difference.

If we were to confine the discussion, for the time being to a data type of string... Can you see the difference between the presence of an empty string and the absence of a string?

If you can, then we could widen the discussion to cover any and all data types. That is why I believe it was necessary to define NULL in the first place - to standardise on a way to represent the presence of an empty "thing" - something that we *know* is empty.

In SQL, NULL is most widely used to represent missing data. I believe it should be possible to store only present data. If a model insists that there be a representation for unknown or absent data then that is a fundamental flaw in the model. Missing, or absent, data should be exactly that - nowhere to be found. It should not be represented at all. It is not, in fact, data.

Regards,
Mike. Received on Thu Nov 24 2005 - 19:34:45 CST

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