Re: grouping in tuple relational calculus

From: Paul <paul_at_test.com>
Date: Thu, 17 Feb 2005 00:39:00 +0000
Message-ID: <4213e7b7$0$53482$ed2619ec@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.

And min and max work on all domains that have an ordering operator (which is most or all of them) whereas sum only works for domains that have an addition operator. So min and max are more "pure" relational than sum, which requires more assistance from the domain.

Paul. Received on Wed Feb 16 2005 - 18:39:00 CST