从mysql数据库删除重复记录只保留其中一条(保留id最小的一条)

准备工作：新建表tb_coupon

/* Navicat Premium Data Transfer Source Server         : root@localhost Source Server Type    : MySQL Source Server Version : 50527 Source Host           : localhost:3306 Source Schema         : leyou Target Server Type    : MySQL Target Server Version : 50527 File Encoding         : 65001 Date: 22/05/2019 18:03:38*/SET NAMES utf8mb4;SET FOREIGN_KEY_CHECKS = 0;-- ------------------------------ Table structure for tb_coupon-- ----------------------------DROP TABLE IF EXISTS `tb_coupon`;CREATE TABLE `tb_coupon`  (  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '优惠卷id',  `name` varchar(20) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL COMMENT '优惠卷名称',  `type` enum('1','2','3') CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL COMMENT '优惠卷类型,1、抵扣  2、折扣(打折）',  `condition` bigint(20) NULL DEFAULT 0 COMMENT '抵扣或折扣条件，如果没有限制，则设置为0',  `reduction` bigint(20) NULL DEFAULT 0 COMMENT '优惠金额',  `discount` int(3) NULL DEFAULT 100 COMMENT '如果没有折扣，为100。如果是八五折，折扣为85',  `targets` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT '' COMMENT '优惠券可以生效的sku的id拼接，以,分割',  `stock` int(6) NOT NULL COMMENT '剩余优惠券数量',  `start_time` datetime NOT NULL COMMENT '优惠券生效时间',  `end_time` datetime NOT NULL COMMENT '优惠券失效时间',  PRIMARY KEY (`id`) USING BTREE) ENGINE = InnoDB AUTO_INCREMENT = 2 CHARACTER SET = utf8 COLLATE = utf8_general_ci COMMENT = '优惠卷表' ROW_FORMAT = Compact;-- ------------------------------ Records of tb_coupon-- ----------------------------INSERT INTO `tb_coupon` VALUES (1, 'uuu', '1', 0, 0, 100, '', 2, '1000-01-01 00:00:00', '1000-01-01 00:00:00');INSERT INTO `tb_coupon` VALUES (2, 'uuu', '1', 0, 0, 100, '', 2, '1000-01-01 00:00:00', '1000-01-01 00:00:00');INSERT INTO `tb_coupon` VALUES (3, 'ddd', '2', 0, 0, 100, '', 2, '1000-01-01 00:00:00', '1000-01-01 00:00:00');INSERT INTO `tb_coupon` VALUES (4, 'ddd', '2', 0, 0, 100, '', 2, '1000-01-01 00:00:00', '1000-01-01 00:00:00');INSERT INTO `tb_coupon` VALUES (5, 'eee', '2', 0, 0, 100, '', 2, '1000-01-01 00:00:00', '1000-01-01 00:00:00');INSERT INTO `tb_coupon` VALUES (6, 'eee', '3', 0, 0, 100, '', 2, '1000-01-01 00:00:00', '1000-01-01 00:00:00');SET FOREIGN_KEY_CHECKS = 1;

1.查出重复的type

SELECT type FROM tb_coupon GROUP BY type HAVING count(type) > 1;

2.查出重复的type数据中最小的id

SELECT min(id) FROM tb_coupon GROUP BY type HAVING count(type) > 1;

3.查出重复的type数据中非最小的id(需要删除的)

SELECT id FROM tb_coupon WHERE type in(    SELECT type FROM tb_coupon GROUP BY type HAVING count(type) > 1)    AND id  not IN(SELECT min(id) FROM tb_coupon GROUP BY type HAVING count(type) > 1);

4.在Mysql中是不能删除查询出来的记录，而是要通过一张临时表来解决

SELECT id from (    SELECT id FROM tb_coupon WHERE type in(        SELECT type FROM tb_coupon GROUP BY type HAVING count(type) > 1)        AND id  not IN(SELECT min(id) FROM tb_coupon GROUP BY type HAVING count(type) > 1)) as t;

5.删除type重复的数据(只保留一条，保留最小id的)

DELETE FROM tb_coupon WHERE id IN (    SELECT id from (        SELECT id FROM tb_coupon WHERE type in(            SELECT type FROM tb_coupon GROUP BY type HAVING count(type) > 1)            AND id  not IN(SELECT min(id) FROM tb_coupon GROUP BY type HAVING count(type) > 1)    ) as t);

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