Re: Why is "group by" obligatory in SQL?
Date: Fri, 24 Jul 2009 14:07:38 -0300
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 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