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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 15:45:47 -0500
Message-ID: <6nsba.117$kh7.6629429@mantis.golden.net>


"Jan Hidders" <jan.hidders_at_REMOVE.THIS.ua.ac.be> wrote in message news:3e6e4547.0_at_news.ruca.ua.ac.be...
> Bob Badour wrote:
> >"Jan Hidders" <jan.hidders_at_REMOVE.THIS.ua.ac.be> wrote in message
> >news:3e6da66b.0_at_news.ruca.ua.ac.be...
> >>
> >> I'm not convinced that bags are never needed. [...] And if you are then
> >> going to simulate them with sets then the cost might become negative
> >> because the set-based optimizer might miss certain optimizations that
> >> would have been easier to spot for a bag-based optimizer.
> >
> >Such as?
>
> Such as combining two iterations over the same bag into one. It's pretty
> easy to see that
>
> SELECT f(x)
> FROM x IN
> SELECT g(y)
> FROM y IN Y
>
> is the same as
>
> SELECT f(g(y))
> FROM y in Y

If we don't have bags, it is not an issue. Is it?

If Y is a relation, the same optimization is available and is just as easy to spot. Received on Tue Mar 11 2003 - 14:45:47 CST

Original text of this message

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