From: Andreas Kretschmer <akretschmer@spamfence.net>
To: pgsql-performance@postgresql.org
Subject: Re: bad execution plan for subselects containing windowing-function
Date: Thu, 14 Jan 2010 19:31:39 +0100
Message-ID: <20100114183139.GA11334@tux> (raw)
In-Reply-To: <20100114180349.GA9962@tux>
References: <20100114170318.GA7634@tux>
<25448.1263489336@sss.pgh.pa.us>
<20100114173025.GA8675@tux>
<25915.1263490925@sss.pgh.pa.us>
<20100114180349.GA9962@tux>
Andreas Kretschmer <akretschmer@spamfence.net> wrote:
> > they are being done over all rows. In this particular example you
> > happen to get the same result, but that's just because "avg(foo) over
> > partition by foo" is a dumb example --- it will necessarily just yield
> > identically foo. In more realistic computations the results would be
> > different.
>
> Okay, i believe you now ;-)
>
> I will try to find a case with different results ...
I have got it!
test=# select * from values;
id | value
----+-------
1 | 10
2 | 20
3 | 30
4 | 40
5 | 50
6 | 60
7 | 70
8 | 80
9 | 90
(9 rows)
Time: 0.240 ms
test=*# select id, sum(value) over (order by id) from values where id = 5;
id | sum
----+-----
5 | 50
(1 row)
Time: 0.352 ms
test=*# select * from (select id, sum(value) over (order by id) from values) foo where id = 5;
id | sum
----+-----
5 | 150
(1 row)
Time: 0.383 ms
Andreas
--
Really, I'm not out to destroy Microsoft. That will just be a completely
unintentional side effect. (Linus Torvalds)
"If I was god, I would recompile penguin with --enable-fly." (unknown)
Kaufbach, Saxony, Germany, Europe. N 51.05082°, E 13.56889°
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To: pgsql-performance@postgresql.org
Cc: akretschmer@spamfence.net
Subject: Re: bad execution plan for subselects containing windowing-function
In-Reply-To: <20100114183139.GA11334@tux>
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