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

From: JOG <jog_at_cs.nott.ac.uk>
Date: 29 Nov 2005 12:46:01 -0800
Message-ID: <1133297161.197857.183420_at_g14g2000cwa.googlegroups.com>


Gene Wirchenko wrote:
[snip]
> >If what does not exist? You think we should have some special value to
>
> The "something" under discussion.
>
> >represent the "fact" that something doesn't exist? Go on then - be fair
>
> No.
>
> Either:
>
> 1) It does not get recorded since a database is statements of what
> we know, or
> 2) The statement is that we know that we do not know something.
> This is a simple boolean value.

D. Rumsfeld made an incredible quote about all of this. Always worth a google. Now, he was dodging questions about Iraq at the time, but amazingly it applies to databases ;) He said:

  • "there are known knowns; there are things we know we know": these are satisfied predicates.
  • "We also know there are known unknowns; that is to say we know there are some things we do not know. ": these should be "unknown_attribute" entries
  • There are also unknown unknowns -- the ones we don't know we don't know.": and you know what, we cannot possibly comment on these, so they are simply not entered ;)
  • But there are also things we know which aren't relevant or just do not tally: "inapplicable_attribute" suffices to handle these. However _in reality_ this means our predicate constraint was wrong. In a perfect world it needs changing.

Cover these and you have covered it all. Just don't mix them up with flipping nulls unless you really can't help it (i.e. you live in an SQL purgatory with the rest of us). Received on Tue Nov 29 2005 - 21:46:01 CET

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