Re: Index not used on group by - Mailing list pgsql-performance

Andrey Repko wrote:
>
>     I have table ma_data, that contain above 300000 rows.
>    This table has primary key id, and field alias_id.
>    I create index (btree)on this field.
>    Set statistic:
>
>  ALTER TABLE "public"."ma_data"
>    ALTER COLUMN "alias_id" SET STATISTICS 998;
>
>    So, when I do something like
>      SELECT alias_id FROM ma_data GROUP BY alias_id

Why are you using GROUP BY without any aggregate functions?

What happens if you use something like
   SELECT DISTINCT alias_id FROM ma_data;

--
   Richard Huxton
   Archonet Ltd