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Re: Expressing SQL in relational algebra

From: Bob Badour <bbadour_at_golden.net>
Date: Sat, 15 Mar 2003 01:20:27 -0500
Message-ID: <U4Aca.79$Qq5.7663675@mantis.golden.net>


"Neo" <neo55592_at_hotmail.com> wrote in message news:4b45d3ad.0303141850.4b00f4a5_at_posting.google.com...
> What might "SELECT * FROM T_Person WHERE (age=20) AND (weight=180);"
> look like if expressed in relational algreba? Any related links would
> be helpful. TIA.

That would depend on the notation. Assuming Years(n) and Pounds(m) are domain selectors for the domains of age and weight, I might write it as:

(T_Person | age=Years(20) AND weight=Pounds(180))

or as:

RESTRICT(T_Person,age=Years(20) AND weight=Pounds(180))

or in _The Third Manifesto_'s Tutorial D syntax:

T_Person WHERE ( age=Years(20) AND weight=Pounds(180) )

You will find many excellent references at: http://www.pgro.uk7.net/books.htm Received on Sat Mar 15 2003 - 00:20:27 CST

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