# Re: NULLs: theoretical problems?

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

Date: Tue, 21 Aug 2007 17:19:04 +0200 (CEST)

Message-ID: <Xns9993732875285vdghher_at_194.177.96.26>

>> > On 20 aug, 17:14, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:

Date: Tue, 21 Aug 2007 17:19:04 +0200 (CEST)

Message-ID: <Xns9993732875285vdghher_at_194.177.96.26>

Jan Hidders <hidders_at_gmail.com> wrote in news: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'. How is it different from what SQL does with unknown values in query predicates ?

> > -- Jan Hidders >Received on Tue Aug 21 2007 - 17:19:04 CEST