Re: The Practical Benefits of the Relational Model
From: Leandro Guimarães Faria Corsetti Dutra <lgcdutra_at_terra.com.br>
Date: Fri, 08 Nov 2002 12:25:38 +0100
Message-ID: <aqg6vi$9nj79$2_at_ID-148886.news.dfncis.de>
Date: Fri, 08 Nov 2002 12:25:38 +0100
Message-ID: <aqg6vi$9nj79$2_at_ID-148886.news.dfncis.de>
Paul Vernon wrote:
> The idea being (I think) that any two projections that have the same
But, they do? The predicate to a relvar would be all its constraints.
Without knowing all the constraints to P and S, we can't know if their
> predicate should also have the same value.
>
> So if we have P (Part PART_#, Part_name STRING) S (Supp SUPPLIER_#,
> Part PART_#)
>
> Then SELECT Part FROM S should equal SELECT Part FROM P
>
> as they have the same predicate.
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