What are the product ids for the problems reported by Christop Berge with closure authorised by Ashley Medhurst?
select product_id from problems as t1 join staff as t2 on t1.reported_by_staff_id = t2.staff_id where t2.staff_first_name = "Christop" and t2.staff_last_name = "Berge" intersect select product_id from problems as t1 join staff as t2 on t1.closure_authorised_by_staff_id = t2.staff_id where t2.staff_first_name = "Ashley" and t2.staff_last_name = "Medhurst"
How many staffs are on the list?
select count ( * ) from staff