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Re: Query Plan - Index Scan & Seq Scan

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: dbadmin(at)nqadmin(dot)com
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: Query Plan - Index Scan & Seq Scan
Date: 2005-05-12 16:05:20
Message-ID: 2052.1115913920@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-admin
Prasanth <dbadmin(at)nqadmin(dot)com> writes:
> A where condition I always use is shown below. This is bringing down the number
> of rows from 6.5m to 1210. I have an index on code also. Even here it is going
> for seq scan.

> EXPLAIN ANALYZE SELECT count(*) fROM a where Code >2;
>                                                           QUERY PLAN
> -------------------------------------------------------------------------------------------------------------------------------
>  Aggregate  (cost=141321.09..141321.09 rows=1 width=0) (actual
> time=6454.063..6454.064 rows=1 loops=1)
>    ->  Seq Scan on a  (cost=0.00..141318.40 rows=1076 width=0) (actual
> time=15.687..6453.292 rows=1210 loops=1)
>          Filter: (code > 2)
>  Total runtime: 6454.140 ms
> (4 rows)

I'm going to hazard a guess that "code" is not of type integer, and that
you're using a pre-8.0 PG release.  Cross-type comparisons are not
indexable before 8.0, so you need to cast the integer constant 2 to
whatever type "code" is.

			regards, tom lane

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