Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?

Home -> Community -> Usenet -> comp.databases.theory -> Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?

From: Bob Badour <bbadour_at_golden.net>
Date: Tue, 11 Mar 2003 14:45:03 -0500
Message-ID: <9urba.103$9b7.6318166@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...
> >> >> >>
> >> >> >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?

I don't need to prove that it is trivial. The onus is on you to prove your original assertion that it is not trivial. Received on Tue Mar 11 2003 - 13:45:03 CST