# 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>

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
>>
>>
>>
>> > 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

Original text of this message