Re: Functional dependency in GROUP BY through JOINs

> From: Simon Riggs [mailto:simon(at)2ndQuadrant(dot)com]
> Sent: 07 December 2012 05:44
> To: David Rowley
> Cc: pgsql-hackers(at)postgresql(dot)org
> Subject: Re: [HACKERS] Functional dependency in GROUP BY through JOINs
>
> On 5 December 2012 23:37, David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
>
> > Though this plan might not be quite as optimal as it could be as it
> > performs the grouping after the join.
>
> PostgreSQL always calculates aggregation as the last step.

I didn't know that was always the case, but it makes sense I guess.
This is probably a bigger project than I imagined it would be then.

>
> It's a well known optimisation to push-down GROUP BY clauses to the lowest
> level, but we don't do that, yet.
>
> You're right that it can make a massive difference to many queries.
>

I agree.

Maybe it'd be something worthwhile for the future then. Perhaps if others
agree it should be something to go on the TODO list?

Regards

David Rowley

> --
> Simon Riggs http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Training & Services