Message-ID: <4F4F6158.7060200@mejor.pl>
Date: Thu, 01 Mar 2012 12:45:28 +0100
From: =?UTF-8?B?TWFyY2luIE1pcm9zxYJhdw==?= <marcin@mejor.pl>
User-Agent: Mozilla/5.0 (X11; Linux x86_64;
	rv:10.0.1) Gecko/20120213 Thunderbird/10.0.1
MIME-Version: 1.0
To: pgsql-performance@postgresql.org
Subject: [planner] Ignore "order by" in subselect if parrent do count(*)
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit

Hello,
my example query (and explain) is:
$ explain SELECT count(*) from (select * from users_profile order by id)
u_p;
                                QUERY PLAN
---------------------------------------------------------------------------
 Aggregate  (cost=1.06..1.07 rows=1 width=0)
   ->  Sort  (cost=1.03..1.03 rows=2 width=572)
         Sort Key: users_profile.id
         ->  Seq Scan on users_profile  (cost=0.00..1.02 rows=2 width=572)
(4 rows)

Meseems "order by id" can be ignored by planner. It should speed up
query without side effect. I know the query should be fixed but this is
real and simplified query from real application.
Does postgresql team think ppostgres should be smarter than user and fix
user queries? If answer is positive please treat this as "feature request".
Thank you and regards,
Marcin.