Martin Nickel wrote:
EXPLAIN SELECT m.mailcode, l.lead_id
FROM mailing m INNER JOIN lead l ON m.mailing_id = l.mailing_id WHERE (m.maildate >= '2005-7-01'::date AND m.maildate < '2005-8-01'::date)
Hash Join  (cost=62.13..2001702.55 rows=2711552 width=20)
  Hash Cond: ("outer".mailing_id = "inner".mailing_id)
  ->  Seq Scan on lead l  (cost=0.00..1804198.60 rows=34065260 width=8)
  ->  Hash  (cost=61.22..61.22 rows=362 width=20)
        ->  Index Scan using mailing_maildate_idx on mailing m  
(cost=0.00..61.22 rows=362 width=20)
              Index Cond: ((maildate >= '2005-07-01'::date) AND (maildate < 
'2005-08-01'::date))


Well the reason *why* is that the planner expects 2.71 million rows to be matched. If that was the case, then a seq-scan of 34 million rows might well make sense. The output from EXPLAIN ANALYSE would show us whether that estimate is correct - is it?

--
  Richard Huxton
  Archonet Ltd

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