On 03/03/2011 05:29 AM, obamabarak@xxxxx wrote:
I use pgsql 9.0.3 and I know that postgresql tries to use the fields in indexes instead of the original table if it possible But when I run SELECT COUNT(id) FROM tab or SELECT COUNT(*) FROM tab where there "id" is PRIMARY KEY and there are other indexes there I get execution plan that doesnt use any indexes, but sequentab scanning the original table. "Aggregate (cost=38685.98..38685.99 rows=1 width=0)" " -> Seq Scan on tab (cost=0.00..36372.38 rows=925438 width=0)" Why is it so?
See here: http://wiki.postgresql.org/wiki/FAQ#Why_is_.22SELECT_count.28.2A.29_FROM_bigtable.3B.22_slow.3F
--- Paul
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