From: Tom Lane <tgl@sss.pgh.pa.us>
To: Marko Niinimaki <manzikki@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: slow subselects
Date: Tue, 20 Feb 2007 02:43:06 -0500
Message-ID: <22952.1171957386@sss.pgh.pa.us> (raw)
In-Reply-To: <58b7e6510702192310v77517652q4ba8ecaf50ea161c@mail.gmail.com>
References: <58b7e6510702192302i6b526e56wee847a2122cec3aa@mail.gmail.com>
<58b7e6510702192310v77517652q4ba8ecaf50ea161c@mail.gmail.com>
"Marko Niinimaki" <manzikki@gmail.com> writes:
> I'm having a surprising performance problem with the following simple
> 'highscore report'
> select studentid, (select max(score) from
> studentprofile prof where prof.studentid = students.studentid) from students;
> I have indexes on students(studentid) and studentprofile(studentid).
The optimal index for this would be on studentprofile(studentid,score).
A quick test says that PG 8.1 knows what to do with such an index ---
what does EXPLAIN show for this query?
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, manzikki@gmail.com
Subject: Re: slow subselects
In-Reply-To: <22952.1171957386@sss.pgh.pa.us>
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