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

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: tjo(at)acm(dot)org
Cc: lists(at)boutiquenumerique(dot)com, pgsql-general(at)postgresql(dot)org
Subject: Re: Does indexing help >= as well as = for integer columns?
Date: 2005-02-01 19:30:39
Message-ID: 18111.1107286239@sss.pgh.pa.us
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"TJ O'Donnell" <tjo(at)acm(dot)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

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