Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?
Date: Mon, 10 Mar 2003 21:56:41 -0500
Message-ID: <GNcba.11$yF5.1462363_at_mantis.golden.net>
"Jan Hidders" <jan.hidders_at_REMOVE.THIS.ua.ac.be> wrote in message
news:3e6cc096.0_at_news.ruca.ua.ac.be...
> Bob Badour wrote:
> >"Jan Hidders" <jan.hidders_at_REMOVE.THIS.ua.ac.be> wrote in message
> >news:3e6c869e.0_at_news.ruca.ua.ac.be...
> >> Bob Badour wrote:
> >> >"Jan Hidders" <jan.hidders_at_REMOVE.THIS.ua.ac.be> wrote in message
> >> >news:3e6bd183.0_at_news.ruca.ua.ac.be...
> >> >> Bob Badour wrote:
> >> >> >"Jan Hidders" <jan.hidders_at_REMOVE.THIS.ua.ac.be> wrote in message
> >> >> >news:3e620dec.0_at_news.ruca.ua.ac.be...
> >> >> >>
> >> >> >> Yes, that too, but mainly that he overestimates the complexity
that
> >> >> >> is added to the optimizer when bags are exposed to the user.
> >> >> >
> >> >> >The optimizer may not be any more complex, but it is nowhere near
as
> >> >> >effective either.
> >> >>
> >> >> No. It can be just as efective.
> >> >
> >> >If that is the case, why haven't they?
> >>
> >> To know if they have or not you would have to be able to compare their
> >> query optimization to that of an existing implementation based on a
> >> set-only approach.
> >
> >Lauri has already provided examples in this thread where one vendor or
> >another has not implemented an available set optimization.
>
> Sure. But what you have to show to support the claim is that those
> optimizations are implemented in DBMSs with a set-only approach. It's not
> enought to show that the algebraic rules are simple because they are also
> not complicated in the bag-approach.
>> >
> >> >> >When I look at your statement above, I think: "Well that totally
> >> >> >invalidates the argument that duplicate removal costs too much in
> >> >> >performance."
> >> >>
> >> >> Why do you think that?
> >> >
> >> >I answered that in the part you snipped. The user will just have to
> >> >formulate and execute multiple queries until the dbms delivers the
> >> >answer the user needs.
> >>
> >> Yes, but how does that invalidate the argument that duplicate removal
> >> sometimes costs too much?
> >You have never established that it costs too much. In order for the user
to
> >get the desired result, the user will eventually have to force the dbms
to
> >remove the duplicates.
>
> If the users doesn't mind the duplicates or knows somehow that there won't
> be any then any time spent on duplicate elimination is wasted.
>
> >> >> >Jan, with all due respect, I cannot count how many times I have
heard
> >> >> >alleged database experts tell users to "Never use DISTINCT." If the
> >> >> >result is already distinct, the keyword should have no cost.
> >> >>
> >> >> Yes. *should* is the right word. Deriving that "at compile time" is
> >> >> not a trival problem.
> >> >
> >> >It is trivial in a system based on sets and requiring logical
identity.
> >>
> >> No, it is just as difficult.
> >
> >The input to every relational operation is a set of distinct tuples with
a
> >given predicate and the output from every relational operation is a set
of
> >distinct tuples with a derivable predicate. Other than projection and
> >summarization, what operations have intermediate duplicate tuples?
>
> The union, if implemented it in a naive way. But is the above somehow
> supposed to be a proof that the problem is trivial?
>> >
> >> >> >Why should they accept any duplicates?
> >> >>
> >> >> I didn't say they should.
> >> >
> >> >You implied that users would more likely accept duplicates with lower
> >> >cardinality.
> >>
> >> would <> should
> >Oh, I see. Deconstructionism again.
>
> The distinction between ontology and deontology is a bit older than that.
>
> >Or are you saying that vendors should ram down their users' throats
> >whatever crap they can get away with ramming?
>
> Try reading what I write and not what you want me to write. That would
help
> the discussion.
I did, and I responded appropriately in both cases. If you want to pretend you did not say what you said, then you are not contributing anything worthwhile. Received on Tue Mar 11 2003 - 03:56:41 CET