Re: Joins with nulls

From: Alfredo Novoa <alfredo_at_ncs.es>
Date: 19 Nov 2002 06:55:38 -0800
Message-ID: <e4330f45.0211190655.6fb167bb@posting.google.com>

> I've read that performing joins with tables that have null values in
> some attributes is a dangerous operation, but no example was given. I
> think that this only can happen if you try to join based on the
> attributes that can have two null values, due to the problem of how to
> interpret null values (are two null values equal?). Can this also
> happen in other circumstances?.

Nulls are not values, are a kind of mark.

Anything with nulls is always dangerous.

See the chapter about missing information of:

http://www.amazon.com/exec/obidos/ASIN/0201709287

Saludos
Alfredo Received on Tue Nov 19 2002 - 08:55:38 CST