您正在寻找FIND_IN_SET

SELECT *
FROM user
WHERE FIND_IN_SET( '2', action_type )

SQL小提琴DEMO

更新

只需提一下，这也是可能的

Just to mentioned it, this is also possible

SELECT *
FROM user
WHERE FIND_IN_SET( 2, action_type )

MySQL将自动转换为char

MySQL will do an automatic conversion to char