Re: Analysis Function

From: David Jarvis <thangalin(at)gmail(dot)com>
To: pgsql-performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Analysis Function
Date: 2010-06-11 00:41:51
Message-ID: AANLkTikZKwBCR8QfGph3aH34A2dJ2NQyOjq-Pt3eZ3_z@mail.gmail.com
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Hi,

I found a slow part of the query:

SELECT
* date(extract(YEAR FROM m.taken)||'-1-1') d1,*
* date(extract(YEAR FROM m.taken)||'-1-31') d2*
FROM
climate.city c,
climate.station s,
climate.station_category sc,
climate.measurement m
WHERE
c.id = 5148 AND ...

Date extraction is 3.2 seconds, but without is 1.5 seconds. The PL/pgSQL
code that actually runs (where p_month1, p_day1, and p_month2, p_day2 are
integers):

* date(extract(YEAR FROM m.taken)||''-'||p_month1||'-'||p_day1||''')
d1,
date(extract(YEAR FROM m.taken)||''-'||p_month2||'-'||p_day2||''')
d2
*
What is a better way to create those dates (without string concatenation, I
presume)?

Dave

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