From: Luiz Rafael Culik Guimaraes <culikr@brturbo.com>
To: pgsql-sql@postgresql.org
Cc: pgsql-general@postgresql.org
Subject: query optimizer dont treat correctly OR
Date: Tue, 27 Apr 2004 11:48:48 -0300
Message-ID: <007101c42c66$c0bffb30$2b38fea9@luiz> (raw)
Hello folks
See the command bellow. I use some thing simmilar about an decade on
Oracle,
Sybase, MSSQL, DB2, etc. But with Postgresql , he generate an FULL TABLE
SCAN,
and consequenyly it take about 10 minutes to run (Very big table..)
----------------------------------------------------------------------
SELECT A.SR_RECNO , A.CDEMP, A.NRPED,A.SR_RECNO
FROM FTB01 A
WHERE ( A.CONTROLE <= ' ' AND A.CDEMP = '75' AND A.NRPED < '0000261' )
OR ( A.CONTROLE = ' ' AND A.CDEMP < '75' )
OR ( A.CONTROLE < ' ' )
ORDER BY A.CDEMP DESC, A.NRPED DESC, A.SR_RECNO DESC
LIMIT 170
----------------------------------------------------------------------
Otherwise, is i write the query on the form of an little more "dummy" and
eliminating the
"OR" and changing by UNION, the time of execution drops to less menos
of two seconds
----------------------------------------------------------------------
SELECT TMP1.* FROM (
SELECT A.SR_RECNO, A.CDEMP, A.NRPED,A.SR_RECNO
FROM FTB01 A WHERE ( A.CONTROLE <= ' ' AND A.CDEMP = '75' AND A.NRPED <
'0000261' )
ORDER BY A.CDEMP DESC, A.NRPED DESC, A.SR_RECNO DESC LIMIT 170 ) TMP1
UNION
SELECT TMP2.* FROM (
SELECT A.SR_RECNO, A.CDEMP, A.NRPED,A.SR_RECNO
FROM FTB01 A WHERE ( A.CONTROLE = ' ' AND A.CDEMP < '75' )
ORDER BY A.CDEMP DESC, A.NRPED DESC, A.SR_RECNO DESC LIMIT 170 ) TMP2
UNION
SELECT TMP3.* FROM (
SELECT A.SR_RECNO, A.CDEMP, A.NRPED,A.SR_RECNO
FROM FTB01 A WHERE OR ( A.CONTROLE < ' ' )
ORDER BY A.CDEMP DESC, A.NRPED DESC, A.SR_RECNO DESC LIMIT 170 ) TMP3
ORDER BY CDEMP DESC, NRPED DESC, SR_RECNO DESC
LIMIT 170
----------------------------------------------------------------------
The comand above works (even being 10 x slower then other Databases
) with our generate the full scan.
Why Post do this wrong julgment with the initial command?
Exist some thing that i can configure to to make postgres works correctly ?
Obs.:
* Tested on versions 7.3.2 e 7.4.1
* Obvialy the vacuumm full analyse was executed
Thanks
Luiz
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-sql@postgresql.org
Cc: culikr@brturbo.com, pgsql-general@postgresql.org
Subject: Re: query optimizer dont treat correctly OR
In-Reply-To: <007101c42c66$c0bffb30$2b38fea9@luiz>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox