How many songs do not have a back vocal?
select count(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"
Show me the titles of those songs.
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"