On 6/4/07, Andrew Sullivan <ajs@xxxxxxxxxxxxxxx> wrote:
On Mon, Jun 04, 2007 at 12:37:42AM +0200, PFC wrote:
> NULL usually means "unknown" or "not applicable"
Aaaargh! No, it doesn't. It means NULL. Nothing else.
If it meant unknown or not applicable or anything else, then
SELECT * FROM nulltbl a, othernulltbl b
WHERE a.nullcol = b.nullcol
would return rows where a.nullcol contained NULL and b.nullcol
contained NULL. But it doesn't, because !(NULL = NULL).
I don't disagree with the principle, but that's a specious argument.
Who says (unknown = unknown) should equal true?
Alexander.
