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

Hugo Kornelis wrote:
[...]
> >>a couple of messages ago, that one of the
> >> rules that form the foundation of SQL is this
> >>
> >> "1. NULLs propagate - any operation that has NULL as one of it's
> >> operands results in NULL."
> >
> >Really ? What about 'FALSE AND NULL' evaluating to FALSE, or 'TRUE OR
> >NULL' evaluating to TRUE ? See the original Codd's truth tables.
>
> AFAIK, there is no NULL in the original Codd's truth tables. Only True,
> False and Unknown.

Please reread the article in order to see that Codd uses letter 'w' to denote both NULL as a missing/unknown value and UNKNOWN as a truth value.

>[...]
Received on Thu Dec 15 2005 - 23:33:16 CET