From: pgsql-general-owner@postgresql.org
[mailto:pgsql-general-owner@postgresql.org] On Behalf Of Michael
Giannakopoulos
Sent: Thursday, November 29, 2012 4:07 PM
To: pgsql-general@postgresql.org
Subject: [GENERAL] About aggregates...
Hello guys,
I would like to ask if there is any way to make an aggregate function to
take a set of tuples as an input variable. I know that an actual aggregate
function receives each tuple one at a time and process it on the fly.
However I want to store tuples in an incremental fashion so as to process
them in a batch approach in the finalaggr function. Think for example
implementing logistic regression (which is an OLAP query by its nature). I
want to support it with the current features that PostgreSQL provides from
which the closest feature is an aggregate. However an aggregate function
feeds me one a tuple for each call, but I would like to have access to a
batch of tuples per function call. Is there any possible way to perform
something like this?
Thank you very much for your time,
Michael
=====================================
Not sure how the system would decide between (1-at-a-time) and
(everything-at-once).
The only approach I can think of would be to build out an array of "tuples"
and then have the aggregate process a single array value each time.
As Ondrej indicates in parallel you can try making use of Windows (probably
with a FRAME definition) as well.
Hopefully this helps but I am not familiar enough with the use-case to be
more specific.
David J.