Re: Aggregation (with GBY) is Relational Division
Date: Mon, 05 Jun 2006 12:07:09 GMT
Message-ID: <N7Vgg.17749$A26.412644_at_ursa-nb00s0.nbnet.nb.ca>
Marshall wrote:
> vadimtro_at_gmail.com wrote:
[snip]
> Actually, I had kind of a jolt reading something Bob Badour
I am surprised that my comment would jolt you. I wonder how you would
define standard deviation without reference to variance, for instance,
or variance without reference to sums of squares etc. I cannot imagine
anyone forsaking the normal definition of average to replace it with
> wrote recently about defining aggregates as either a fold
> or an expression written in terms of folds. (He did not use
> the term "fold".) Thus, avg(x) can be defined as simply
> sum(x) / count(). And sum(x) can be defined as simply
> fold(x,+,0).
>
> I like that much better. For one thing, it makes it much
> easier to eliminate duplicate folds in a complex group-by.
> (It's hard to explain why, so I won't bother. It's not clear
> if this post will interest anyone anyway, the OP excepted. :-)
(I am not even sure how I would express that mathematically without
using recursion.)
>>From a programming language standpoint, it raises the
> question of handling the aggregate expressions. But
> that's not any theoretical difficulty, and not necessarily
> all that much design difficulty.
I wonder what you would call arbitrary expressions defined in terms of aggregates if you did not call them aggregates. Received on Mon Jun 05 2006 - 14:07:09 CEST