Message-Id: <199805141321.PAA04595@gate.va.fh-ulm.de>
From: "Olaf Mittelstaedt" <mstaedt@va-sigi.va.fh-ulm.de>
Organization: Verwaltung FH Ulm
To: pgsql-interfaces@postgresql.org
Date: Thu, 14 May 1998 15:20:56 +0100
MIME-Version: 1.0
Content-type: text/plain; charset=US-ASCII
Content-transfer-encoding: 7BIT
Subject: Index unused with OR?
Priority: normal

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.