参考资料

• MySQL的连接查询：left join , right join , join
• MySQL 日期和时间戳的转换 | 以及DATE_FORMAT()用法_慌途L-CSDN博客_mysql时间戳转日期
• MySQL根据某字段分组（group by）之后再根据另外的字段排序（order by）

数据库表

CREATE TABLE `buy` (
  `id` varchar(50) NOT NULL COMMENT 'id',
  `buy_cost` int(11) NOT NULL COMMENT '购买花费',
  `buy_expirationDate` date NOT NULL COMMENT '过期日期',
  `buy_date` date NOT NULL,
  `buy_leaseTime` int(11) NOT NULL COMMENT '购买有效期',
  `user_id` varchar(50) NOT NULL COMMENT '用户id',
  `music_id` varchar(50) NOT NULL COMMENT '歌曲id',
  PRIMARY KEY (`id`,`user_id`,`music_id`),
  KEY `fk_user_has_music_music1_idx` (`music_id`),
  KEY `fk_user_has_music_user1_idx` (`user_id`),
  CONSTRAINT `fk_user_has_music_music1` FOREIGN KEY (`music_id`) REFERENCES `music` (`id`),
  CONSTRAINT `fk_user_has_music_user1` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

需求

　　先根据music_id将buy表中的数据分为一组，然后取这组中buy_expirationDate最靠后的数据。

解决方案

SELECT a.* FROM buy a INNER JOIN
(SELECT max( UNIX_TIMESTAMP(buy_expirationDate) ) max_date,music_id
FROM buy GROUP BY music_id) b
ON a.music_id = b.music_id AND UNIX_TIMESTAMP(a.buy_expirationDate) = b.max_date