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From: "Eric" <emayo@pozicom.net>
X-Newsgroups: comp.databases.postgresql.sql
Subject: 2 Selects 1 is faster, why?
Date: Tue, 25 Jun 2002 15:25:32 -0400
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If I perform the following 2 selects, the first one is EXTREMELY slow where
the 2nd one is very fast.

(1) Slow

select
  o.orderid,
  ol.itemcode,
  ol.itemname

from
  orders o,
  orlines ol

where
  o.orderid = '1234' and
  ol.orderid = o.orderid;

(2) VERY FAST

select
  o.orderid,
  ol.itemcode,
  ol.itemname

from
  orders o,
  orlines ol

where
  o.orderid = '1234' and
  ol.orderid = '1234'

Why would 2 be so much faster?  I have ran the EXPLAIN on this and index
scans are being used.

NOTE: The actual queries return more information than this, but the
fundamental change shown above seems to give me the instant response I am
looking for. (1) takes about 60 seconds to run and (2) takes 3-5 seconds to
run.

Thanks, Eric