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

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