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
*/


www.devze.com-- ----------------------------
-- 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
)
;

-- ----------------------------
-- Rhttp://www.devze.comecords 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
-- -----------www.devze.com-----------------
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 ,co开发者_oracleunt(1)  from test g编程客栈roup by name  having count(1)>1

输出.

name        couwww.devze.comnt

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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