Task: Text to Code
Input (English): SQL: SELECT T1.Title FROM Songs AS T1 WHERE T1.SongId NOT IN ( SELECT T2.SongId FROM Tracklists AS T2 )
Feedback: Make sure that songs does not have a back vocal .
Output (English): SELECT DISTINCT title FROM vocals AS t1 JOIN songs AS t2 ON t1.songid  =  t2.songid EXCEPT SELECT t2.title FROM vocals AS t1 JOIN songs AS t2 ON t1.songid  =  t2.songid WHERE TYPE  =  "back"