Show me engineers each staff has contacted. List the names of contact staff and engineers.
select t1.staff_name, 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 group by t1.staff_name
How many engineers did each staff contact? List the count instead of the names of engineers.
select t1.staff_name, count(*) from staff as t1 join engineer_visits as t2 on t1.staff_id = t2.contact_staff_id group by t1.staff_name