Re: Aggregates and associated relational operators

"Bob Badour" <bbadour_at_golden.net> wrote in message news:oK96b.557$Lp.53402758_at_mantis.golden.net...
> "Mikito Harakiri" <mikharakiri_at_ywho.com> wrote in message
> news:ry86b.30$pP2.101_at_news.oracle.com...
> > Some time ago there has been already a small thread about broken
symmetry
> > among relational operators ("Naisetrac Product", which BTW should
properly
> > called "Tensor Product"). Recent discussion about "fundamental"
aggregates
> > satisfying identities like this:
> >
> > sum(a union b) = sum(a) + sum(b)
>
> Am I missing something? I don't recall anyone suggesting the above
identity,
> and it seems to me the identity would be:
>
> sum(a union b) = sum(a) + sum(b) - sum(a intersect b)
>
> Are you using multiset union?
>
>
> > max(a union b) = max(max(a),max(b))
>
>
> > prompts a related question:
> > Why union operator is so special that it has associated aggregation? Is
> > there anything similar to aggregation that is missing?
>
> I do not understand the questions. Could you clarify them a little?

Agreed. With your correction, if I use sets, then the aggregate identity is no longer similar among different aggregates, nor it makes "union" special. I also understand that multisets wouldn't be interested to at least part of the audience:-( Received on Sat Sep 06 2003 - 01:18:04 CEST