Re: object algebra
From: Jonathan Leffler <jleffler_at_earthlink.net>
Date: Thu, 04 Mar 2004 03:17:31 GMT
Message-ID: <fdx1c.18170$yZ1.5662_at_newsread2.news.pas.earthlink.net>
Date: Thu, 04 Mar 2004 03:17:31 GMT
Message-ID: <fdx1c.18170$yZ1.5662_at_newsread2.news.pas.earthlink.net>
Neo wrote:
>>You're confusing missing information and nulls.
> RDM creates NULLs when information required by a tuple is missing.
Can you illustrate? Which operator(s) create(s) nulls? Are you sure that operator is in the TTM version of the RDM? Which version of the RDM are you assuming - or, if you prefer, whose exposition of the RDM are you using?
Note that TTM does not include any OUTER JOIN operator which generates nulls (or any other operator that generates nulls, for that matter - so I think the answer to the third question is necessarily 'No').
-- Jonathan Leffler #include <disclaimer.h> Email: jleffler_at_earthlink.net, jleffler_at_us.ibm.com Guardian of DBD::Informix v2003.04 -- http://dbi.perl.org/Received on Thu Mar 04 2004 - 04:17:31 CET