Re: NULLs: theoretical problems?
From: Jan Hidders <hidders_at_gmail.com>
Date: Mon, 20 Aug 2007 21:39:58 -0000
Message-ID: <1187645998.798282.58960_at_g4g2000hsf.googlegroups.com>
Date: Mon, 20 Aug 2007 21:39:58 -0000
Message-ID: <1187645998.798282.58960_at_g4g2000hsf.googlegroups.com>
On 20 aug, 17:14, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:
> Jan Hidders <hidd..._at_gmail.com> wrote in news:1187599195.269472.153110
> _at_a39g2000hsc.googlegroups.com:
>
> > On 20 aug, 01:48, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:
> >> I wonder what the truth tables for 'AND' and 'OR' would look like with
> >> the DEF operator. Could you show those tables ?
>
> > They would be the usual table you already gave:
>
> >> x y AND
> >> -------
> >> defined
> >> 0 0 0
> >> 1 0 0
> >> 0 1 0
> >> 1 1 1
>
> What is 'x AND y' equal to if x is '1' and y is not defined ?
The database would not allow you to write that. If y is nullable then it forces you to write "DEF y : x AND y".
- Jan Hidders