Hi,
Based on an entry in the mailing list from 30 Oct 2001
about efficient deletes on subqueries,
I've found two ways to do so (PostgreSQL 7.2.1):
1.
BEGIN ;
EXPLAIN ANALYZE
DELETE FROM onfvalue WHERE EXISTS(
SELECT * FROM onfvalue j WHERE
j.sid= 5 AND
onfvalue.lid = j.lid AND
onfvalue.mid = j.mid AND
onfvalue.timepoint = j.timepoint AND
onfvalue.entrancetime < j.entrancetime
) ;
ROLLBACK ;
QUERY PLAN:
Seq Scan on onfvalue
(cost=0.00..805528.05 rows=66669 width=6)
(actual time=61.84..25361.82 rows=24 loops=1) SubPlan -> Index Scan using advncd_onfvalue_idx_stlme on onfvalue j
(cost=0.00..6.02 rows=1 width=36) (actual time=0.14..0.14 rows=0 loops=133338)
Total runtime: 25364.76 msec
2.
BEGIN ;
EXPLAIN ANALYZE
INSERT INTO temprefentrancetime(timepoint,lid,mid,sid,entrancetime)
SELECT o.timepoint,o.lid,o.mid,o.sid,o.entrancetime
FROM onfvalue o join onfvalue j ON (
o.lid = j.lid AND
o.mid = j.mid AND
o.timepoint = j.timepoint AND
o.entrancetime < j.entrancetime
) WHERE o.sid= 5 ;
EXPLAIN ANALYZE
DELETE FROM onfvalue WHERE
onfvalue.timepoint = temprefentrancetime.timepoint AND
onfvalue.mid = temprefentrancetime.mid AND
onfvalue.lid = temprefentrancetime.lid AND
onfvalue.sid = temprefentrancetime.sid AND
onfvalue.entrancetime = temprefentrancetime.entrancetime ;
DELETE FROM temprefentrancetime;
ROLLBACK ;
QUERY PLAN:
Merge Join
(cost=16083.12..16418.36 rows=4 width=52)
(actual time=17728.06..19325.02 rows=24 loops=1) -> Sort (cost=2152.53..2152.53 rows=667 width=28) (actual
time=1937.70..2066.46rows=16850 loops=1) -> Index Scan using advncd_onfvalue_idx_stlme on onfvalue o
(cost=0.00..2121.26rows=667 width=28) (actual time=0.57..709.89 rows=16850 loops=1) -> Sort (cost=13930.60..13930.60
rows=133338width=24) (actual time=13986.07..14997.43 rows=133110 loops=1) -> Seq Scan on onfvalue j
(cost=0.00..2580.38rows=133338 width=24) (actual time=0.15..3301.06 rows=133338 loops=1)
Total runtime: 19487.49 msec
QUERY PLAN:
Nested Loop
(cost=0.00..6064.40 rows=1 width=62)
(actual time=1.34..8.32 rows=24 loops=1) -> Seq Scan on temprefentrancetime (cost=0.00..20.00 rows=1000 width=28)
(actualtime=0.44..1.07 rows=24 loops=1) -> Index Scan using advncd_onfvalue_idx_stlme on onfvalue (cost=0.00..6.02
rows=1width=34) (actual time=0.22..0.25 rows=1 loops=24)
Total runtime: 10.15 msec
The questions are:
Is there a way to put the second form (more complicated, but faster)
in one statement?
Or is there even a third way to delete, which I cannot see?
Regards, Christoph