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This article introduces the relevant knowledge of "how to solve the left connection problem of MySQL". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Two tables, one user, one user_log

CREATE TABLE `user` (`id` int (11) NOT NULL AUTO_INCREMENT, `name` varchar (20) DEFAULT NULL, PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8;CREATE TABLE `user` (`id` int (10) NOT NULL, `user_ id` int (10) NOT NULL, `log_ time` timestamp NOT NULL DEFAULT '0000-00-0000: 00varchar 0000, `message`varchar (30) NOT NULL, PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8;INSERT INTO `user` VALUES (' 1mm, 'wang') INSERT INTO `user`VALUES ('2clients,' meng'); INSERT INTO `user`VALUES ('3clients,' zhang') -Records of user_log-- INSERT INTO `user_ log` VALUES ('1mm,' 1mm, '2017-07-20 1313 user_ 07mm,' some data') INSERT INTO `user_ log` VALUES ('2mm,' 1mm, '2017-07-27 13 VALUES 13 VALUES,' some data'); INSERT INTO `Log `VALUES ('3 miles,'1 bike, '2017-07-28 13 13 VALUES 07,' some data'); INSERT INTO `Log` VALUES ('4 miles,'1 bike, '2017-08-26 13 VALUES 11 VALUES,' some data') INSERT INTO `user_ log` VALUES ('5mm,' 1mm, '2017-08-26 17 VALUES 11VALUES,' some data'); INSERT INTO `Log 'VALUES (' 6mm, '1mm,' 2017-08-27 13 VALUES 11VALUES, 'some data')

That's it.

SELECT U.N., UL.LOG_TIME, UL.MESSAGE FROM USER U LEFT JOIN USER_LOG UL ON U.ID = UL.USER_ID AND (UL.LOG_TIME > '2017-09-01 07 UL.MESSAGE FROM USER U LEFT JOIN USER_LOG UL ON U.ID 13 UL.MESSAGE FROM USER U LEFT JOIN USER_LOG UL ON U.ID 07' OR UL.LOG_TIME IS NULL) WHERE U.ID = 1

Just put and behind left join on.

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