MySQL去重保留最大的那条记录（取最新的记录）

 1 SET NAMES utf8mb4;

 2 SET FOREIGN_KEY_CHECKS = ;

 3

 4 -- ----------------------------

 5 -- Table structure for t_login_log

 6 -- ----------------------------

 7 DROP TABLE IF EXISTS `t_login_log`;

 8 CREATE TABLE `t_login_log` (

 9   `id` int() NOT NULL AUTO_INCREMENT,

10   `user_id` int() NOT NULL COMMENT '用户ID',

11   `device_name` varchar() COLLATE utf8mb4_bin NOT NULL COMMENT '登录设备',

12   `login_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '登录时间',

13   PRIMARY KEY (`id`)

14 ) ENGINE=InnoDB AUTO_INCREMENT= DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;

15

16 -- ----------------------------

17 -- Records of t_login_log

18 -- ----------------------------

19 BEGIN;

20 INSERT INTO `t_login_log` VALUES (, , 'iPhone 6s', '2019-07-01 19:20:25');

21 INSERT INTO `t_login_log` VALUES (, , 'vivo x20', '2019-06-28 16:21:11');

22 INSERT INTO `t_login_log` VALUES (, , 'huawei P30', '2019-07-04 19:21:59');

23 INSERT INTO `t_login_log` VALUES (, , 'vivo x20', '2019-06-30 19:22:34');

24 INSERT INTO `t_login_log` VALUES (, , 'vivo x20', '2019-07-04 19:23:07');

25 INSERT INTO `t_login_log` VALUES (, , 'iPad mini', '2019-07-03 19:23:25');

26 INSERT INTO `t_login_log` VALUES (, , 'iPhone 8 Plus', '2019-06-30 19:24:06');

27 INSERT INTO `t_login_log` VALUES (, , 'MI8', '2019-07-03 19:25:00');

28 COMMIT;

29

30 SET FOREIGN_KEY_CHECKS = ; 

1 SELECT * FROM t_login_log ORDER BY user_id;

2

3 SELECT

4 	t1.*

5 FROM t_login_log t1

6 	LEFT JOIN t_login_log t2 ON t1.user_id = t2.user_id AND t1.login_time < t2.login_time

7 WHERE t2.id IS NULL;