# Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?

From: Mikito Harakiri <mikharakiri_at_ywho.com>

Date: Tue, 11 Mar 2003 13:16:42 -0800

Message-ID: <Fssba.12$pX3.148_at_news.oracle.com>

Date: Tue, 11 Mar 2003 13:16:42 -0800

Message-ID: <Fssba.12$pX3.148_at_news.oracle.com>

"Jan Hidders" <jan.hidders_at_REMOVE.THIS.ua.ac.be> wrote in message news:3e6e4547.0_at_news.ruca.ua.ac.be...

> Such as combining two iterations over the same bag into one. It's pretty

*> easy to see that
**>
**> SELECT f(x)
**> FROM x IN
**> SELECT g(y)
**> FROM y IN Y
**>
**> is the same as
**>
**> SELECT f(g(y))
**> FROM y in Y
**>
**> which is a simple straightforward rule in bag algebra.
*

Let XY be

x y

- -

1 1

1 2

2 3

Then,

select x from XY

where x in (select y from XY)

returns 1 and 2

while

select y from XY

returns

1,1, and 2

Or my SQL interpretation of your formulas is wrong? Received on Tue Mar 11 2003 - 22:16:42 CET