SQL开发知识：postgresql如何 删除重复数据
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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