postgresql 删除重复数据案例详解

1.建表

/*
 navicat premium data transfer

 source server         : localhost
 source server type    : postgresql
 source server version : 110012
 source host           : localhost:5432
 source catalog        : postgres
 source schema         : public

 target server type    : postgresql
 target server version : 110012
 file encoding         : 65001

 date: 30/07/2021 10:10:04
*/


-- ----------------------------
-- table structure for test
-- ----------------------------
drop table if exists "public"."test";
create table "public"."test" (
  "id" int4 not null default null,
  "name" varchar(255) collate "pg_catalog"."default" default null,
  "age" int4 default null
)
;

-- ----------------------------
-- records of test
-- ----------------------------
insert into "public"."test" values (1, 'da', 1);
insert into "public"."test" values (2, 'da', 12);
insert into "public"."test" values (3, 'dd', 80);
insert into "public"."test" values (4, 'dd', 80);
insert into "public"."test" values (5, 'd1', 13);

-- ----------------------------
-- primary key structure for table test
-- ----------------------------
alter table "public"."test" add constraint "test_pkey" primary key ("id");

2.根据名称获取重复

先看看哪些数据重复了

select name ,count(1)  from test group by name  having count(1)>1

输出.

name        count

da              2

dd              2

3.删除所有重复数据

注意把要更新的几列数据查询出来做为一个第三方表，然后筛选更新。

delete from test where name in (select t.name from (select name ,count(1)  from test group by name  having count(1)>1) t)

4.保留一行数据

这里展示我们需要保留的数据：重复数据，保留id最大那一条

select
 1. 
from
 test 
where
 id not in (
 ( select min( id ) as id from test group by name ) 
 )

5.删除数据

delete 
from
 test 
where
 id not in (
 select
  t.id 
 from
 ( select max( id ) as id from test group by name ) t 
 )

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