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;