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
);