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
Find the last names of teachers who are not involved in any detention.
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
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
Find the last names of teachers who are not involved in any detention .