Why relational division is so uncommon?

[Vadim Tropashko]

http://vadimtropashko.wordpress.com/...s-so-uncommon/

[V.J. Kumar]

Vadim Tropashko <va************ **@yahoo.comwro te in
news:11******** **************@ t39g2000prd.goo glegroups.com:

http://vadimtropashko.wordpress.com/...on-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.

[jefftyzzer]

On Apr 25, 11:16 am, Vadim Tropashko <vadimtro_inva. [e-mail]>
wrote:

http://vadimtropashko.wordpress.com/...sion-is-so-unc...

In my experience, those "find (exactly) matching sets" type questions
are particularly tricky. On the subject of Rel Div, I thought Itzik
Ben-Gan's June and July '03 articles in SQL Server Magazine were
exemplary:

July 2003
A Different Setup
When your query needs to find items with certain relationships, you
can use relational division, or you can try these new tricks.

June 2003
Set Members and Relationships
You can use Set Theory to identify groups of items that have a certain
relationship to other items.

Looking forward to the receipt of your book ("it's in the mail").

--Jeff