Sleeves ใดมี Back of Unknown?ไม่จำเป็นต้องใช้ตารางทั้งหมด
Which Sleeves have a Back of Unknown?It is not neccessary to use all the tables.
 table_name_72:  (sleeves [ VARCHAR ] back [ VARCHAR) ]
SELECT sleeves FROM table_name_72 WHERE back = "unknown"