Have many engineers that were contacted by each manager?
select count ( t3.first_name ) from staff as t1 join engineer_visits as t2 on t1.staff_id = t2.contact_staff_id join maintenance_engineers as t3 on t2.engineer_id = t3.engineer_id
First and Last name, please.
select t3.first_name, t3.last_name from staff as t1 join engineer_visits as t2 on t1.staff_id = t2.contact_staff_id join maintenance_engineers as t3 on t2.engineer_id = t3.engineer_id