postgresql 刪除重復(fù)數(shù)據(jù)案例詳解
發(fā)布日期：2022-01-21 17:34 | 文章來源：CSDN
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.根據(jù)名稱獲取重復(fù)
先看看哪些數(shù)據(jù)重復(fù)了
select name ,count(1) from test group by name having count(1)>1
輸出.
name count
da 2
dd 2
3.刪除所有重復(fù)數(shù)據(jù)
注意把要更新的幾列數(shù)據(jù)查詢出來做為一個第三方表，然后篩選更新。
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.保留一行數(shù)據(jù)
這里展示我們需要保留的數(shù)據(jù)：重復(fù)數(shù)據(jù)，保留ID最大那一條
SELECT 1. FROM test WHERE id NOT IN ( ( SELECT min( id ) AS id FROM test GROUP BY name ) )
5.刪除數(shù)據(jù)
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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