For each reservation, find the base price and the actual rate payed.
select t1.rate, t2.baseprice from reservations as t1 join rooms as t2 on t1.room = t2.roomid
How many times did the actual price exceeded the base price?
select count(*) from reservations as t1 join rooms as t2 on t1.room = t2.roomid where t1.rate - t2.baseprice > 0
What are the first and last names of people who payed more than the rooms' base prices?
select t1.firstname, t1.lastname from reservations as t1 join rooms as t2 on t1.room = t2.roomid where t1.rate - t2.baseprice > 0