Re: Why is "group by" obligatory in SQL?

From: Bob Badour <>
Date: Fri, 24 Jul 2009 14:07:38 -0300
Message-ID: <4a69ea60$0$23754$>

paul c wrote:

> Cimode wrote:

>> Snipped..
>>> I suspect that what a 'TRDBMS' is, isn't yet fully known.  Lots of open
>>> questions, here're just a few:
>>> - Codd espoused logical data independence, yet by assuming some
>>> relations couldn't be updated in certain ways, he allowed a kind of
>>> contradiction, or at least a kind of dead-end.
>> That is unclear.  Unfortunately we can't ask Codd for that.
>> ...

> Right, it becomes our problem It is very clear that he allowed
> 'inserts' wrt some relations but not 'deletes', and vice-versa for other
> relations. That is a big loophole if you ask me, like when you ask one
> of the locals for directions to the next town and he answers "you can't
> get there from here". Contradicts what Codd called relational closure.

Where exactly did he do this? It's something you have mentioned several times, but I am unfamiliar with the reference.

>>> - where is the constraint theory?  will normalization turn out to be
>>> just a small part of this?
>> I would not state exactly that way.  I know for a fact that solving
>> the problem of constraint specialization representation simplifies
>> normalization up to a point where it is not normalization anymore, at
>> least not in the traditional sense of a cumbersome process.

> I would say that the 'constraint problem' hasn't even been defined. Date
> took some baby steps by trying to classify different kinds of
> constraints. But sometimes such baby steps obscure the forest.
> Normalization is very much about information structure and I think it
> would be more practical to try to formalize the scope of constraints. If
> that could be done, then perhaps the constant question of 'where'
> constraints should be applied, eg., application or dbms would be
> clearer. (I don't believe the question is as obvious as many RT
> advocates suggest, there is more to it than trying to make sure the dbms
> is authoritative.)

Such as? If you are going to say performance, then I would point out the dbms needs to extend to the client computer to enforce constraints without a round-trip to some server. Received on Fri Jul 24 2009 - 19:07:38 CEST

Original text of this message