1.数据初始化：
test=# create table deltest(id int, name varchar(255));
CREATE TABLE
test=# create table deltest_bk (like deltest);
CREATE TABLE
test=# insert into deltest select generate_series(1, 10000), 'ZhangSan';
INSERT 0 10000
test=# insert into deltest select generate_series(1, 10000), 'ZhangSan';
INSERT 0 10000
test=# insert into deltest_bk select * from deltest;
2.常规方法
test=# explain analyse delete from deltest a where a.ctid <> (select min(t.ctid) from deltest t where a.id=t.id);
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------
Delete on deltest a (cost=0.00..195616.30 rows=1518 width=6) (actual time=67758.866..67758.866 rows=0 loops=1)
-> Seq Scan on deltest a (cost=0.00..195616.30 rows=1518 width=6) (actual time=32896.517..67663.228 rows=10000 loops=1)
Filter: (ctid <> (SubPlan 1))
Rows Removed by Filter: 10000
SubPlan 1
-> Aggregate (cost=128.10..128.10 rows=1 width=6) (actual time=3.374..3.374 rows=1 loops=20000)
-> Seq Scan on deltest t (cost=0.00..128.07 rows=8 width=6) (actual time=0.831..3.344 rows=2 loops=20000)
Filter: (a.id = id)
Rows Removed by Filter: 19998
Total runtime: 67758.931 ms
test=# select count(*) from deltest;
count
-------
10000
(1 行记录)
3.使用NOT IN
test=# truncate table deltest;
TRUNCATE TABLE
test=# insert into deltest select * from deltest_bk;
INSERT 0 20000
test=# explain analyse delete from deltest a where a.ctid not in (select min(ctid) from deltest group by id);
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------
Delete on deltest a (cost=131.89..2930.46 rows=763 width=6) (actual time=30942.496..30942.496 rows=0 loops=1)
-> Seq Scan on deltest a (cost=131.89..2930.46 rows=763 width=6) (actual time=10186.296..30814.366 rows=10000 loops=1)
Filter: (NOT (SubPlan 1))
Rows Removed by Filter: 10000
SubPlan 1
-> Materialize (cost=131.89..134.89 rows=200 width=10) (actual time=0.001..0.471 rows=7500 loops=20000)
-> HashAggregate (cost=131.89..133.89 rows=200 width=10) (actual time=10.568..13.584 rows=10000 loops=1)
-> Seq Scan on deltest (cost=0.00..124.26 rows=1526 width=10) (actual time=0.006..3.829 rows=20000 loops=1)
Total runtime: 30942.819 ms
(9 行记录)
test=# select count(*) from deltest;
count
-------
10000
(1 行记录)
4.使用OVER
test=# truncate table deltest;
TRUNCATE TABLE
test=# insert into deltest select * from deltest_bk;
INSERT 0 20000
test=# explain analyze delete from deltest a
where a.ctid = any(array (select ctid from (select row_number() over (partition by id), ctid from deltest) t where t.row_number > 1));
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------
Delete on deltest a (cost=250.74..270.84 rows=10 width=6) (actual time=98.363..98.363 rows=0 loops=1)
InitPlan 1 (returns $0)
-> Subquery Scan on t (cost=204.95..250.73 rows=509 width=6) (actual time=29.446..47.867 rows=10000 loops=1)
Filter: (t.row_number > 1)
Rows Removed by Filter: 10000
-> WindowAgg (cost=204.95..231.66 rows=1526 width=10) (actual time=29.436..44.790 rows=20000 loops=1)
-> Sort (cost=204.95..208.77 rows=1526 width=10) (actual time=12.466..13.754 rows=20000 loops=1)
Sort Key: deltest.id
Sort Method: quicksort Memory: 1294kB
-> Seq Scan on deltest (cost=0.00..124.26 rows=1526 width=10) (actual time=0.021..5.110 rows=20000 loops=1)
-> Tid Scan on deltest a (cost=0.01..20.11 rows=10 width=6) (actual time=82.983..88.751 rows=10000 loops=1)
TID Cond: (ctid = ANY ($0))
Total runtime: 98.912 ms
(13 行记录)
test=# select count(*) from deltest;
count
-------
10000
(1 行记录)
