MySQL CONCAT opposite

csv - What is the opposite of GROUP_CONCAT in MySQL? - Stack Overflow
https://stackoverflow.com/questions/17308669/what-is-the-opposite-of-group-concat-in-mysql

MySQL :: Reverse command for GROUP_CONCAT or SET
https://forums.mysql.com/read.php?10,391462

MySQL :: MySQL 5.7 Reference Manual :: 12.5 String Functions
https://dev.mysql.com/doc/refman/5.7/en/string-functions.html

MySQL的行转列、列转行、连接字符串函数用法_百度经验
https://jingyan.baidu.com/article/75ab0bcbca7c23d6864db2cf.html