数据库教程: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 = 0;   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(11) not null auto_increment,  10   `user_id` int(11) not null comment '用户id',  11   `device_name` varchar(32) 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=9 default charset=utf8mb4 collate=utf8mb4_bin;  15   16 -- ----------------------------  17 -- records of t_login_log  18 -- ----------------------------  19 begin;  20 insert into `t_login_log` values (1, 1121, 'iphone 6s', '2019-07-01 19:20:25');  21 insert into `t_login_log` values (2, 2120, 'vivo x20', '2019-06-28 16:21:11');  22 insert into `t_login_log` values (3, 1607, 'huawei p30', '2019-07-04 19:21:59');  23 insert into `t_login_log` values (4, 2120, 'vivo x20', '2019-06-30 19:22:34');  24 insert into `t_login_log` values (5, 2120, 'vivo x20', '2019-07-04 19:23:07');  25 insert into `t_login_log` values (6, 1121, 'ipad mini', '2019-07-03 19:23:25');  26 insert into `t_login_log` values (7, 1607, 'iphone 8 plus', '2019-06-30 19:24:06');  27 insert into `t_login_log` values (8, 1970, 'mi8', '2019-07-03 19:25:00');  28 commit;  29   30 set foreign_key_checks = 1; 

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;