SELECT last_name FROM Teachers EXCEPT SELECT T1.last_name FROM Teachers AS T1 JOIN Detention AS T2 ON T1.teacher_id = T2.teacher_id
Temukan nama belakang guru yang tidak terlibat dalam penahanan apa pun.
CREATE TABLE Teachers (last_name VARCHAR); CREATE TABLE Teachers (last_name VARCHAR, teacher_id VARCHAR); CREATE TABLE Detention (teacher_id VARCHAR)