Re: NULLs: theoretical problems?

From: V.J. Kumar <vjkmail_at_gmail.com>
Date: Fri, 24 Aug 2007 13:50:12 +0200 (CEST)
Message-ID: <Xns99964FB886C21vdghher@194.177.96.26>

Jan Hidders <hidders_at_gmail.com> wrote in news:1187906563.506451.71800_at_q3g2000prf.googlegroups.com:

> On 23 aug, 23:27, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:

>> Let's take a look at it. Could you give a query example and you
>> interpretration of the DEF construct therein  ?

>
> SELECT * FROM t WHERE DEF t.a : (t.a = 5 OR TRUE);
>
> is not equivalent with
>
> SELECT * FROM t WHERE t.a = 5 OR TRUE;

I do not understand why they are not equivalent.

The first SQL predicate, according to your rules, evaluates to 'true': 'DEF t.a : (t.a = 5 OR TRUE)' -> 'FALSE OR TRUE' -> 'TRUE'

The second SQL predicate also evaluates to 'true': 't.a = 5 OR TRUE' -> 'UNKNOWN OR TRUE' -> 'TRUE'

What is the difference ? Received on Fri Aug 24 2007 - 06:50:12 CDT