How many student are involved in any kind of accident?
select count ( * ) from students where student_id in ( select student_id from behavior_incident )
How about student not involved in any kind of incident?
select count ( * ) from students where student_id not in ( select student_id from behavior_incident )
And what are their names?
select first_name, middle_name, last_name from students where student_id not in ( select student_id from behavior_incident )