To: "Merlin Moncure" <mmoncure@gmail.com>
cc: "Postgresql Performance" <pgsql-performance@postgresql.org>
Subject: Re: is it possible to make this faster? 
In-reply-to: <b42b73150605260956h30a960efl39d75601d5767747@mail.gmail.com> 
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	<b42b73150605252147h218ec25ci183283334731adbd@mail.gmail.com>
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	<b42b73150605260956h30a960efl39d75601d5767747@mail.gmail.com>
Comments: In-reply-to "Merlin Moncure" <mmoncure@gmail.com>
	message dated "Fri, 26 May 2006 12:56:44 -0400"
Date: Fri, 26 May 2006 13:07:39 -0400
Message-ID: <27137.1148663259@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

"Merlin Moncure" <mmoncure@gmail.com> writes:
> did you have a key on a,b,c?

Yeah, I did
	create index t1i on t1 (a,b,c);
Do I need to use some other syntax to get it to work?

> select count(*) from (select a,b,max(c) group by a,b) q;
> blows the high performance case as does putting the query in a view.

I noticed that too, while trying to suppress the returning of the
results for timing purposes ... still a few bugs in their optimizer
obviously.  (Curiously, EXPLAIN still claims that the index is being
used.)

> mysql> select user_id, acc_id, max(sample_date) from usage_samples group by 1,2
> [...]
> +---------+--------+------------------+
> 939 rows in set (0.07 sec)

> mysql> select user_id, acc_id, max(sample_date) from usage_samples group by 1,2
> [...]
> +---------+--------+------------------+--------------+
> 939 rows in set (1.39 sec)

I don't understand what you did differently in those two cases?
Or was there a DROP INDEX between?

			regards, tom lane