Re: Why relational division is so uncommon?
Date: 26 Apr 2007 03:08:35 +0200
Message-ID: <Xns991DD71403396vdghher_at_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 ?
"
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
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.
"