CREATE TABLE performance (songid NUMBER, bandmate NUMBER, stageposition CLOB)
CREATE TABLE instruments (songid NUMBER, bandmateid NUMBER, instrument CLOB)
CREATE TABLE tracklists (albumid NUMBER, position NUMBER, songid NUMBER)
CREATE TABLE band (id NUMBER, firstname CLOB, lastname CLOB)
CREATE TABLE albums (aid NUMBER, title CLOB, year NUMBER, label CLOB, type CLOB)
CREATE TABLE songs (songid NUMBER, title CLOB)
CREATE TABLE vocals (songid NUMBER, bandmate NUMBER, type CLOB)

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" "t1" JOIN "songs" "t2" ON "t1"."songid" = "t2"."songid" EXCEPT SELECT "t2"."title" FROM "vocals" "t1" JOIN "songs" "t2" ON "t1"."songid" = "t2"."songid" WHERE "back" = "type"