Question: Find the last names of teachers who are not involved in any detention.
Schema: create table teachers (last_name varchar, PRIMARY KEY (last_name)); create table teachers (last_name varchar, teacher_id varchar, PRIMARY KEY (last_name)); create table detention (teacher_id varchar, PRIMARY KEY (teacher_id))
SQL: 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