Hi all,
consider this view:
CREATE OR REPLACE VIEW v_current_connection AS
SELECT ul.id_user
FROM user_login ul,
current_connection cc
WHERE ul.id_user = cc.id_user;
And this is the explain on a usage of that view:
# explain select * from v_current_connection_test where
sp_connected_test(id_user) = FALSE;
QUERY PLAN
----------------------------------------------------------------------------------------------------------
Hash Join (cost=42.79..1325.14 rows=451 width=5)
Hash Cond: ("outer".id_user = "inner".id_user)
-> Seq Scan on user_login ul (cost=0.00..1142.72 rows=27024 width=4)
Filter: (sp_connected_test(id_user) = false)
-> Hash (cost=40.49..40.49 rows=919 width=5)
-> Index Scan using idx_connected on current_connection cc
(cost=0.00..40.49 rows=919 width=5)
Index Cond: (connected = true)
(7 rows)
apart my initial surprise to see that function applied at rows not returned by
the view
( Tom Lane explained me that the planner is able to push down the outer
condition )
why postgres doesn't apply that function at table current_connection given the
fact are extimated
only 919 vs 27024 rows?
redefining the view:
CREATE OR REPLACE VIEW v_current_connection AS
SELECT cc.id_user
FROM user_login ul,
current_connection cc
WHERE ul.id_user = cc.id_user;
then I obtain the "desidered" plan.
# explain select * from v_current_connection_test where
sp_connected_test(id_user ) = FALSE;
QUERY PLAN
----------------------------------------------------------------------------------------------------------
Hash Join (cost=46.23..1193.47 rows=452 width=5)
Hash Cond: ("outer".id_user = "inner".id_user)
-> Seq Scan on user_login ul (cost=0.00..872.48 rows=54048 width=4)
-> Hash (cost=45.08..45.08 rows=460 width=5)
-> Index Scan using idx_connected on current_connection cc
(cost=0.00..45.08 rows=460 width=5)
Index Cond: (connected = true)
Filter: (sp_connected_test(id_user) = false)
(7 rows)
Is not possible in any way push postgres to apply that function to the right
table ?
Shall I rewrite the views figuring out wich column is better to expose ?
Regards
Gaetano Mendola
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