[PERFORM] Index not used on group by

[Andrey Repko]

Hello all,

    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
   and have (with seq_scan off):
   
   Group  (cost=0.00..1140280.63 rows=32 width=4) (actual time=0.159..2640.090 
rows=32 loops=1)
      ->  Index Scan using reference_9_fk on ma_data  (cost=0.00..1139526.57 
rows=301624 width=4) (actual time=0.120..1471.128 rows=301624 loops=1)
    Total runtime: 2640.407 ms
   (3 rows)

   As I understand there are some problems with visibility of records,
   but some others DBMS used indexes without problems(for example
   FireBird)? Or maybe some another information be helpful for me and
   community.

-- 
С наилучшими пожеланиями,
  Репко Андрей Владимирович       mailto:[EMAIL PROTECTED]


---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match