K C Lau wrote:
Thank you all for your suggestions. I' tried, with some variations too, but still no success. The times given are the best of a few repeated tries on an 8.1 beta 2 db freshly migrated from 8.0.3 on Windows.



A small denormalization, where you mark the row with the latest atdate for each playerid may get you the performance you want.

e.g: (8.1beta1)

ALTER TABLE player ADD islastatdate boolean;

UPDATE player SET islastatdate = true where (playerid,atdate) IN
(SELECT playerid, atdate FROM vcurplayer);

CREATE OR REPLACE VIEW vcurplayer AS
SELECT * FROM player a
WHERE islastatdate;

CREATE INDEX player_id_lastatdate ON player(playerid, islastatdate)
WHERE islastatdate;

ANALYZE player;

Generating some test data produced:

EXPLAIN ANALYZE
SELECT playerid,atdate
FROM vcurplayer
WHERE playerid='22220';

QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------
Index Scan using player_id_lastatdate on player a (cost=0.00..4.33 rows=1 width=13) (actual time=0.142..0.149 rows=1 loops=1)
   Index Cond: ((playerid = '22220'::text) AND (lastatdate = true))
   Filter: lastatdate
 Total runtime: 0.272 ms
(4 rows)

Whereas with the original view definition:

CREATE OR REPLACE VIEW vcurplayer AS
SELECT * FROM player a
WHERE a.atdate =
( SELECT max(b.atdate) FROM player b
  WHERE a.playerid = b.playerid);

EXPLAIN ANALYZE
SELECT playerid,atdate
FROM vcurplayer
WHERE playerid='22220';

QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------------------
Index Scan using player_id_date on player a (cost=0.00..7399.23 rows=11 width=13) (actual time=121.738..121.745 rows=1 loops=1)
   Index Cond: (playerid = '22220'::text)
   Filter: (atdate = (subplan))
   SubPlan
-> Result (cost=1.72..1.73 rows=1 width=0) (actual time=0.044..0.047 rows=1 loops=2000)
           InitPlan
-> Limit (cost=0.00..1.72 rows=1 width=4) (actual time=0.028..0.031 rows=1 loops=2000) -> Index Scan Backward using player_id_date on player b (cost=0.00..3787.94 rows=2198 width=4) (actual time=0.019..0.019 rows=1 loops=2000)
                         Index Cond: ($0 = playerid)
                         Filter: (atdate IS NOT NULL)
 Total runtime: 121.916 ms
(11 rows)

Note that my generated data has too many rows for each playerid, but the difference in performance should illustrate the idea.

Cheers

Mark

---------------------------(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

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