Re: Another view on analysis and ER
From: Jonathan Leffler <jleffler_at_earthlink.net>
Date: Thu, 06 Dec 2007 15:32:48 -0800
Message-ID: <13lh1laan1uod62_at_corp.supernews.com>
>
> Keys are, but key /primacy/ is not. If one ignores any performance
> differences between a primary key and any other key (as of course one
> should, although it may not be possible in current SQL systems), the
> remaining difference is merely syntactical convenience---hardly a
> logical issue.
Date: Thu, 06 Dec 2007 15:32:48 -0800
Message-ID: <13lh1laan1uod62_at_corp.supernews.com>
Jon Heggland wrote:
> Quoth Bob Badour:
>> Keys and references are logical issues and not physical issues. Physical >> issues affect only performance.
>
> Keys are, but key /primacy/ is not. If one ignores any performance
> differences between a primary key and any other key (as of course one
> should, although it may not be possible in current SQL systems), the
> remaining difference is merely syntactical convenience---hardly a
> logical issue.
Consider a database containing a relation containing information about 'the elements' - as in hydrogen, helium, etc.
The elements table has 3 keys (candidate keys):
Element name Atomic number Element symbol
-- Jonathan Leffler #include <disclaimer.h> Email: jleffler_at_earthlink.net, jleffler_at_us.ibm.com Guardian of DBD::Informix v2007.0914 -- http://dbi.perl.org/ publictimestamp.org/ptb/PTB-1963 sha224 2007-12-06 21:00:03 0AC762E1452FAE2896292EA605A8D66B9FEE09F8E55C0B87073F31DAReceived on Fri Dec 07 2007 - 00:32:48 CET