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  • 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

     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; 

    自连接,取最新的记录

    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; 

    效果

     

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  • 原文地址:https://www.cnblogs.com/cjsblog/p/11134518.html
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