From: Jan Dvorak
Date: November 30 2000 7:51pm
Subject: Re: Index with condition? [A distant idea]
List-Archive: http://lists.mysql.com/internals/166
Message-Id: <3A26AFD8.C00FE6DD@veda.cz>
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Hi Monty,

It's great to have this confimed!
And let Informix and Oracle know. :-)

Jan

P.S.
Sorry for my delayed reply.
Lots of work these days...



Michael Widenius wrote:
> 
> Hi!
> 
> Do you still remember this discussion:
> 
> Jan> I know Informix a little bit.
> Jan> Their server is basically in two possible modes:
> Jan>  * online: serving clients.
> Jan>  * quiescent: checking and repairing dbspaces.
> Jan> When the server is brought up, it enters the quiescent mode
> Jan> and "mounts" all the dbspaces it should work with.
> Jan> Only when it's ready, it enters the online mode.
> Jan> If you pass an option to the server,
> Jan> it only does the quiescent part and then exits.
> Jan> This way, they could get rid of standalone utilities for the check & repair.
> 
> Jan> I'm not saying MySQL should go this direction.
> Jan> After all, MySQL's data files are very different in nature from Informix's dbspaces
> Jan> (those can be raw devices or cooked files, but the structure is page-oriented,
> Jan> just like Oracle).
> 
> I just asked a guy from the ANSI SQL standard committee about this.
> 
> I mailed the following example to him and asked if it was according to
> the standard to accept the following rows WITHOUT any errors:
> 
> -------
> create table crash_q (a int, b int, unique (a,b));
> insert into crash_q values (1,1);
> insert into crash_q values (1,null);
> insert into crash_q values (1,null);
> ----------
> 
> His answer was:
> 
> 'Your interpretation of the semantics of null values and unique constraints is
>  correct. A null value in any uniqueness column will cause that row not to be
>  considered a duplicate of any other row'
> 
> It looks like Informix and Oracle are not following the standard in
> this case...
> 
> Anyway, I have added a test for this in crash-me so that we can get
> some more information about this next time we run it.
> 
> Regards,
> Monty