List the states and counts of staff living there.
select t1.state_province_county, count(*) from addresses as t1 join staff as t2 on t1.address_id = t2.staff_address_id group by t2.staff_id
List the states which have between 2 to 4 staff living there.
select t1.state_province_county from addresses as t1 join staff as t2 on t1.address_id = t2.staff_address_id group by t1.state_province_county having count(*) between 2 and 4;