Re: Very simple question to relational theorists.

Ok!

> So if the wff R(A,B,...) denotes the predicate for R then the wff for R RENAME A TO N is R(N,B,...). If the wff S(X,Y,...,A,...) denotes the predicate for S then the wff for (R JOIN S) RENAME A TO N is R(N,B,...) AND S(X,Y,...,N,...).

Below is my previous unanswered question (with some comment after //...). Really I cannot understand where is difference here

Suppose I have two relation
A( a1, a2, ...)
and
B( b1, b2, ...)
I use some JOIN and RENAME operations to produce new C relation form the two ones C(c1, c2, ...)

//So, C is result of operation A RENAME a1 TO c1 ... JOIN B RENAME b1 TO cn... //what is equal to opearion (A JOIN B) RENAME...

My questions again.

Am I right that I can can use any new names c1, c2 if they are distinct?

Can I use some mnemonic rules (only mnemonic!) to form the names c... of attributes of C relation from the names of attributes of A and B relations? For example name с1 is string "a1.b1"?

Philip, where is difference? Received on Fri Sep 07 2012 - 18:02:40 CEST