mysql GROUP_CONCAT 以及 其逆過程

新建多選選項表types 以及 選擇結果表 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');

一個多選結果分拆成多行單選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

一個多選結果對應其相應的多選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;

問題反思：當選項個數超過10 ， LOCATE(a.types,b.multiSelect)>0會將1,10+ 同時查詢到，使用的時候 請添加相應的限制條件