Re: Seq Scan

On Jun 1, 2007, at 11:48 , Tyler Durden wrote:

> I'm having some problems in performance in a simple select count(id)
> from....

Unrestricted count() (i.e., no WHERE clause) will perform a
sequential scan. If you're looking for faster ways to store table row
count information, please search the archives, as this has been
discussed many times before.

> # explain select (id) from table_name;
> -[ RECORD
> 1 ]----------------------------------------------------------------
> QUERY PLAN | Seq Scan on table_name (cost=0.00..8601.30
> rows=266730 width=4)

The query returns the id column value for each row in the table. The
fastest way to do this is visiting every row., i.e., a sequential
scan. Using an index would require (1) looking in the index and (2)
looking up the corresponding row.

Michael Glaesemann
grzm seespotcode net