Assuming I have the tables student
, club
, and student_club
:
student {
id
name
}
club {
id
name
}
stude
-- EXPLAIN ANALYZE
WITH two AS (
SELECT c0.student_id
FROM tmp.student_club c0
, tmp.student_club c1
WHERE c0.student_id = c1.student_id
AND c0.club_id = 30
AND c1.club_id = 50
)
SELECT st.* FROM tmp.student st
JOIN two ON (two.student_id=st.id)
;
The query plan:
Hash Join (cost=1904.76..1919.09 rows=337 width=15) (actual time=6.937..8.771 rows=324 loops=1)
Hash Cond: (two.student_id = st.id)
CTE two
-> Hash Join (cost=849.97..1645.76 rows=337 width=4) (actual time=4.932..6.488 rows=324 loops=1)
Hash Cond: (c1.student_id = c0.student_id)
-> Bitmap Heap Scan on student_club c1 (cost=32.76..796.94 rows=1614 width=4) (actual time=0.667..1.835 rows=1646 loops=1)
Recheck Cond: (club_id = 50)
-> Bitmap Index Scan on sc_club_id_idx (cost=0.00..32.36 rows=1614 width=0) (actual time=0.473..0.473 rows=1646 loops=1)
Index Cond: (club_id = 50)
-> Hash (cost=797.00..797.00 rows=1617 width=4) (actual time=4.203..4.203 rows=1620 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 57kB
-> Bitmap Heap Scan on student_club c0 (cost=32.79..797.00 rows=1617 width=4) (actual time=0.663..3.596 rows=1620 loops=1)
Recheck Cond: (club_id = 30)
-> Bitmap Index Scan on sc_club_id_idx (cost=0.00..32.38 rows=1617 width=0) (actual time=0.469..0.469 rows=1620 loops=1)
Index Cond: (club_id = 30)
-> CTE Scan on two (cost=0.00..6.74 rows=337 width=4) (actual time=4.935..6.591 rows=324 loops=1)
-> Hash (cost=159.00..159.00 rows=8000 width=15) (actual time=1.979..1.979 rows=8000 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 374kB
-> Seq Scan on student st (cost=0.00..159.00 rows=8000 width=15) (actual time=0.093..0.759 rows=8000 loops=1)
Total runtime: 8.989 ms
(20 rows)
So it still seems to want the seq scan on student.