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

"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 - 15:16:42 CST