MySQL去重保留最大的那条记录（取最新的记录）

-- 以用户登录日志表为例，取用户最近登录的设备

 

SET NAMES utf8mb4;

SET FOREIGN_KEY_CHECKS = 0;

 

 -- ----------------------------

 -- Table structure for t_login_log

 -- ----------------------------

 DROP TABLE IF EXISTS `t_login_log`;

 CREATE TABLE `t_login_log` (

   `id` INT(11) NOT NULL AUTO_INCREMENT,

   `user_id` INT(11) NOT NULL COMMENT '用户ID',

   `device_name` VARCHAR(32) COLLATE utf8mb4_bin NOT NULL COMMENT '登录设备',

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

   PRIMARY KEY (`id`)

 ) ENGINE=INNODB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;

 

 -- ----------------------------

 -- Records of t_login_log

 -- ----------------------------

 BEGIN;

 INSERT INTO `t_login_log` VALUES (1, 1121, 'iPhone 6s', '2019-07-01 19:20:25');

 INSERT INTO `t_login_log` VALUES (2, 2120, 'vivo x20', '2019-06-28 16:21:11');

 INSERT INTO `t_login_log` VALUES (3, 1607, 'huawei P30', '2019-07-04 19:21:59');

 INSERT INTO `t_login_log` VALUES (4, 2120, 'vivo x20', '2019-06-30 19:22:34');

 INSERT INTO `t_login_log` VALUES (5, 2120, 'vivo x20', '2019-07-04 19:23:07');

 INSERT INTO `t_login_log` VALUES (6, 1121, 'iPad mini', '2019-07-03 19:23:25');

 INSERT INTO `t_login_log` VALUES (7, 1607, 'iPhone 8 Plus', '2019-06-30 19:24:06');

 INSERT INTO `t_login_log` VALUES (8, 1970, 'MI8', '2019-07-03 19:25:00');

 COMMIT;

 

 SET FOREIGN_KEY_CHECKS = 1; 

 

-- 自连接，取最新的记录

SELECT * FROM t_login_log ORDER BY user_id;

 

SELECT 

  t1.* 

 FROM t_login_log t1

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

 WHERE t2.id IS NULL;