Horton

Re: Does indexing help >= as well as = for integer columns?

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: tjo@acm.org
Cc: lists@boutiquenumerique.com, pgsql-general@postgresql.org
Date: 2005-02-01T19:30:39Z
Lists: pgsql-general 
"TJ O'Donnell" <tjo@acm.org> writes:
> This I don't get.  Why is an index scan not used?  Isn't an index supposed
> to help when using > < >= <= too?
> Explain Analyze Select count(smiles) from structure where _c >= 30
> Aggregate  (cost=196033.74..196033.74 rows=1 width=32) (actual time=42133.432..42133.434 rows=1
> loops=1)
>   ->  Seq Scan on structure  (cost=0.00..191619.56 rows=1765669 width=32) (actual
> time=8050.437..42117.062 rows=1569 loops=1)
>         Filter: (_c >= 30)

Have you ANALYZEd the table lately?  That rowcount estimate is off by
about three orders of magnitude :-(

			regards, tom lane