mysql GROUP_CONCAT 以及 其逆过程

新建多选选项表types 以及 选择结果表 user_MultiSelect

DROP TABLE IF EXISTS `types`;
 
CREATE TABLE `types` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `types` smallint(6) NOT NULL,
  `comment` varchar(10) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=25 DEFAULT CHARSET=utf8;
 
/*Data for the table `types` */
 
insert  into `types`(`id`,`types`,`comment`) values 
 
(1,1,'a'),
 
(2,2,'b'),
 
(3,3,'c'),
 
(4,4,'d'),
 
(5,5,'e'),
 
(6,6,'f'),
 
(7,7,'g'),
 
(8,8,'h'),
 
(9,9,'i'),
 
(10,10,'j');
 
/*Table structure for table `user_MultiSelect` */
 
DROP TABLE IF EXISTS `user_MultiSelect`;
 
CREATE TABLE `user_MultiSelect` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `userId` int(11) NOT NULL,
  `multiSelect` varchar(20) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;
 
/*Data for the table `user_MultiSelect` */
 
insert  into `user_MultiSelect`(`id`,`userId`,`multiSelect`) values 
 
(1,1,'1,2,3,'),
 
(2,2,'2,'),
 
(3,3,'5,6,7,'),
 
(4,7,'4,5'),
 
(5,9,'8,9,'),
 
(6,11,'10');

一个多选结果分拆成多行单选comment

SELECT b.id,a.`types`,a.comment,b.multiSelect
FROM `types`  a LEFT JOIN `user_MultiSelect` b ON LOCATE(a.types,b.multiSelect)>0  

一个多选结果对应其相应的多选comment

SELECT b.id,GROUP_CONCAT(a.comment),b.multiSelect
FROM `types`  a LEFT JOIN `user_MultiSelect` b ON LOCATE(a.types,b.multiSelect)>0  
GROUP BY b.id;

问题反思：当选项个数超过10 ， LOCATE(a.types,b.multiSelect)>0会将1,10+ 同时查询到，使用的时候 请添加相应的限制条件