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

In article <7mg9p1ta4a4makhurqf54n60rli117d4sn_at_4ax.com>, hugo_at_pe_NO_rFact.in_SPAM_fo says...
> >> >Yes, I know. But that doesn't jive with what database textbooks teach:
> >> >That constraints are assertions that hold true for all possible values
> >> >of the database.
> >>
> >> Then these textbooks are wrong.
> >
> >Yes, given that they talk about SQL. If they talk about the relational
> >model in a more abstract manner, what then?
>
> Then they might be correct. If there's any formal and widely accepted
> definition of "constraint" in the context of (non-SQL) relational model,
> I'm not aware of it.

I'd look to the textbooks for such a definition. :) To let SQL define the relational model would be very backwards.

-- 
Jon