# Re: NULLs: theoretical problems?

From: V.J. Kumar <vjkmail_at_gmail.com>

Date: Tue, 21 Aug 2007 22:20:03 +0200 (CEST)

Message-ID: <Xns9993A62FF46D6vdghher_at_194.177.96.26>

>> > On 21 aug, 01:13, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:

>

> No. There is no conversion necessary. That's the whole point.

Date: Tue, 21 Aug 2007 22:20:03 +0200 (CEST)

Message-ID: <Xns9993A62FF46D6vdghher_at_194.177.96.26>

Jan Hidders <hidders_at_gmail.com> wrote in news:1187723867.532149.53830_at_57g2000hsv.googlegroups.com:

> On 21 aug, 17:19, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:

*>> Jan Hidders <hidd..._at_gmail.com> wrote**>> innews:1187699645.789970.23980_at_57g2000hsv.googlegroups.com:**>>**>>**>>*>> > On 21 aug, 01:13, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:

*>> >> Jan Hidders <hidd..._at_gmail.com> wrote**>> >> innews: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".**>>**>> >> What is DEF y : x AND y equal to if x is '1' and y is not defined**>> >> ?**>>**>> > False. Because DEF y : f(y) means that (1) y is defined and (2)**>> > f(y) holds.**>>**>> So you convert undefined operands in your logical formulas to**>> 'false'.*>

> No. There is no conversion necessary. That's the whole point.

I do not understand. You have:

1 1 1 (1) 1 0 0 (2) 0 0 (3)

So 'DEF y:y' will give the same result when y is either undefined or 'false', rows (2) and (3). How is it not substituting 'false' for undefined ?

> > -- Jan Hidders > >Received on Tue Aug 21 2007 - 22:20:03 CEST