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Re: Why relational division is so uncommon?

From: V.J. Kumar <vjkmail_at_gmail.com>
Date: 26 Apr 2007 03:08:35 +0200
Message-ID: <Xns991DD71403396vdghher@217.22.228.20>


Vadim Tropashko <vadimtro_invalid_at_yahoo.com> wrote in news:1177525004.714698.115410_at_t39g2000prd.googlegroups.com:

> http://vadimtropashko.wordpress.com/why-relational-division-is-so-uncom
> mon/

You wrote: "Informally, Relational Division corresponds to the any quantifier in calculus, which should be as frequent as its exists counterpart!"

In which calculus ? In SQL, ANY is a synonym for SOME (see a SQL reference). In spoken English, ANY can be interpreted either universally or existentially. Perhaps, you've meant FORALL ?

"
In a word, it one of the most distinguished relational database features referential integrity that undermines a possibility for a non vacuous relational division query.
"

That's a strange conclusion based on a trivial Emp/Dept schema ! I hope you are not denying that relational division can be quite useful to express some queries. Consider a query: what patients have all of such and so symptoms, or any similar question.

The problems with the r.d. are that it arguably cannot be implemented efficiently and is not as easy to understand as a typical SPJ query. Received on Wed Apr 25 2007 - 20:08:35 CDT

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