Find songs that have a lead vocal.
select distinct title from vocals as t1 join songs as t2 on t1.songid = t2.songid where type = "lead"
Find all other 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 = "lead"