Re: grouping in tuple relational calculus

"Paul" <paul_at_test.com> wrote in message news:4213e7b7$0$53482$ed2619ec_at_ptn-nntp-reader03.plus.net...
> Mikito Harakiri wrote:
> > Speaking of aggregates, I always wondered why some aggregates are
> > expressable by standard means (min, max can be expressed as antijoins),
> > while the others aren't (sum).
>
> I guess that min and max only require an ordering, which is a more
> fundamental concept than addition, which is required for sum.

That's right, on one hand, aggregate min and max are based upon lattice join and meet binary operators, similar to sum based upon binary addition. This makes all of them to fit into aggregate framework. On the other hand, lattice implies order, and with order one can leverage antijoin. Received on Thu Feb 17 2005 - 02:21:54 CET