Re: Functional dependencies and GROUP BY

On Sun, Jul 18, 2010 at 02:40, Peter Eisentraut <peter_e(at)gmx(dot)net> wrote:
> On lör, 2010-07-17 at 11:13 -0600, Alex Hunsaker wrote:
>> So I would expect the more indexes you
>> had or group by items to slow it down.  Not so much the number of
>> columns.  Right?
>
> At the outer level (which is not visible in this patch) it loops over
> all columns in the select list, and then it looks up the indexes each
> time.  So the concern was that if the select list was * with a wide
> table, looking up the indexes each time would be slow.

Thanks for the explanation.

>> Anyhow it sounds like I should try it on top of the other patch and
>> see if it works.  I assume it might still need some fixups to work
>> with that other patch? Or do you expect it to just work?
>
> There is some work necessary to integrate the two.

I just read that patch is getting pushed till at least the next commit
fest: http://archives.postgresql.org/pgsql-hackers/2010-07/msg01219.php

Should we push this patch back to? Alternatively we could make it
work with just primary keys until the other patch gets in. I think
that makes sense, find that attached. Thoughts?

Note I axed the index not null attribute checking, I have not thought
to deeply about it other than if its a primary key it cant have non
null attributes.... Right? I may have missed something subtle hence
the heads up.