Re: Question about slow Select when using 'IN'.

Mike Winter <mike.winter@*nospam**frontlogic.com> writes:
> My query is of the form:
> SELECT col, count(col) FROM tab WHERE id IN (3,
> 4,7,2, ...) GROUP BY COL ORDER BY count
> for a very large number of rows.

> I have an index on id, so the explain looks like:

> Aggregate  (cost=12.12..12.14 rows=1 width=5)
>   ->  Group  (cost=12.12..12.13 rows=4 width=5)
>         ->  Sort  (cost=12.12..12.12 rows=4 width=5)
>               ->  Index Scan using col_id_idx2, col_id_idx2, col_id_idx2,
> col_id_idx2 on tab  (cost=0.00..12.08 rows=4 width=5)

The planner obviously does not think this is a large table (the cost
estimates correspond to very small numbers of pages).  I wonder
whether you have ever VACUUMed or ANALYZEd the table.
        regards, tom lane