From: Olaf Mittelstaedt <mstaedt@va-sigi.va.fh-ulm.de>
To: pgsql-interfaces@postgresql.org
Subject: Index unused with OR?
Date: Thu, 14 May 1998 15:20:56 +0100
Message-ID: <199805141321.PAA04595@gate.va.fh-ulm.de> (raw)
Hello all,
playing around with the latest ODBC driver I noticed very slow
answers when using OR with an indexed column in the WHERE part
of a SELECT.
To verify this I tried the following directly with psql on the
database server:
postgres=> create database test7;
CREATEDB
postgres=> \c test7
connecting to new database: test7
test7=> create table t7(i1 int4,i2 int4);
CREATE
test7=> create unique index i_t7 on t7(i1);
CREATE
test7=> insert into t7 values(1,2);
INSERT 53741 1
test7=> insert into t7 values(2,3);
INSERT 53742 1
test7=> insert into t7 values(3,4);
INSERT 53743 1
test7=> explain select * from t7 where i1=1;
NOTICE: QUERY PLAN:
Index Scan on t7 (cost=0.00 size=0 width=8)
EXPLAIN
test7=> explain select * from t7 where (i1=1) or (i1=2);
NOTICE: QUERY PLAN:
Seq Scan on t7 (cost=0.00 size=0 width=8)
EXPLAIN
Obviously the index isn't used. Both PostgreSQL 6.3.1 and 6.3.2 are
suffering from this problem.
Any help or hints?
Regards,
Olaf
--
Olaf Mittelstaedt - IuK - mittelstaedt@fh-ulm.de
Fachhochschule Ulm Prittwitzstr. 10 89075 Ulm
Tel.: +49 (0)731-502-8220 Fax: -8270
Nemo me impune lacessit.
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To: pgsql-interfaces@postgresql.org
Cc: mstaedt@va-sigi.va.fh-ulm.de
Subject: Re: Index unused with OR?
In-Reply-To: <199805141321.PAA04595@gate.va.fh-ulm.de>
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