Re: help needed -- sequential scan problem

sarlav kumar <sarlavk@yahoo.com> writes:
> I have a query which does not use index scan unless I force postgres to use index scan. I dont want to force
postgres,unless there is no way of optimizing this query. 

The major issue seems to be in the sub-selects:

>                  ->  Seq Scan on merchant_purchase mp  (cost=0.00..95.39 rows=44 width=4) (actual time=2.37..2.58
rows=6loops=619) 
>                        Filter: (merchant_id = $0)

where the estimated row count is a factor of 7 too high.  If the
estimated row count were even a little lower, it'd probably have gone
for an indexscan.  You might get some results from increasing the
statistics target for merchant_purchase.merchant_id.  If that doesn't
help, I'd think about reducing random_page_cost a little bit.

            regards, tom lane