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

"Steve Kass" <skass_at_drew.edu> wrote in message news:b3ga4e$4nh$1_at_slb0.atl.mindspring.net...
> >Yes, it has. But how are you going to express in your algebra that you
are
> >not going to eliminate duplicates immediately after a projection?
> >
> >
> Do you mean "are going to eliminate", meaning duplicate a_i ?
> Given { (<101, 'abc'>, 3), (<102, 'abc'>, 2)}, a projection onto
> the second column naively gives { (<'abc'>, 3), (<'abc'>, 2)}.
> Since we might not want multiple representations of a bag of
> 5 'abc's, we can aggregate after set-like projection or make
> aggregation a part of bag projection, analogous to a
> non-bag algebra's need to eliminate duplicates.

How about

{ (<101, 'abc'>, 2), (<102, 'abc'>, 2)} Received on Tue Feb 25 2003 - 12:32:05 CST