Find the name of songs that does not have a back vocal.
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"
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"
[{'Nenhum': 'Nenhum resultado encontrado'}]