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

From: paul c <>
Date: Fri, 24 Jul 2009 17:22:29 GMT
Message-ID: <p5mam.37976$PH1.26582_at_edtnps82>

Bob Badour wrote:

>> 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.
> ...

In his 1990 book, in one of the later chapters (around chapter 20 if I recall, haven't got the pdf right now) to do with views, he basically agrees with what Hugh Darwen says about inserting to a union. Admittedly, he didn't call this a contradiction, but it is there nonetheless!

... (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.

I didn't have performance in mind. It was more that leading to my attitude that the 'client computer' notion is a very unproductive one. I would rather think of peer engines, maybe this is a llittle like the way X-windows conceptualizes the 'client' as a 'server'. Optimization is another question. It seems to me that when most people talk about constraints they start off on the wrong foot, assuming optimization is the immediate question, I'd say it's usually best to start with a conceptual framework before talking about performance problems. I only mention X-windows because it has a clear starting concept with similar perforrmance issues and there might be lessons to be learned from that. Received on Fri Jul 24 2009 - 19:22:29 CEST

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