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Re: Sql to Relational Algebra

From: Bob Badour <bbadour_at_golden.net>
Date: Mon, 21 Jul 2003 11:59:06 -0400
Message-ID: <23VSa.1120$qy3.189016155@mantis.golden.net>


"Roy Hann" <rhann_at_globalnet.co.uk> wrote in message news:bfgecs$kvb$1_at_sparta.btinternet.com...
> "Bob Badour" <bbadour_at_golden.net> wrote in message
> news:brnSa.1072$jp6.179816497_at_mantis.golden.net...
> [snip]
> >
> > The latter advantage is particularly important for usability. Years ago,
> > Fabian Pascal did a comparison of different SQL dbms's ability to
provide
> > good, consistent performance for logically equivalent queries using
> > different redundant elements of SQL. If I recall correctly, the dbms
that
> > could achieve the fastest performance would also deliver the worst
> > performance depending on how the user expressed the query. Ingres
> delivered
> > the most consistent performance because, at the time, it supported SQL
by
> > translating it to QUEL.
>
> I am never one to downplay Ingres' manifold virtues, but let me point out
> that the last statement above stopped being true more than a decade ago.

As I said, Fabian wrote the essay years ago.

> Ingres only briefly translated SQL into QUEL. That was the approach taken
> in the later versions of Release 5, which came out in the late eighties.
> Since Release 6, and onwards, Ingres processes SQL directly (although QUEL
> is still fully supported).

I had heard that Ingres foolishly gave up this advantage.

> Ingres still does an excellent job of translating SQL queries into a
> canonical form that leads to the same (optimal) plan.

<snip>

> Bob's statement is not entirely incorrect though.

My statement was not incorrect in any way, shape or form. Fabian wrote the essay when I said he wrote the essay, and, at the time, Ingres achieved its consistent performance by translating SQL to QUEL.

The point in my earlier post was not about Ingres but was an answer to a question regarding the advantages of translating SQL to a direct representation of the relational algebra. There are, of course, many advantages to doing so, and the person asking the question hit upon a major advantage for which published empirical evidence has existed for well over a decade. Received on Mon Jul 21 2003 - 10:59:06 CDT

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