How many reservations were made for each room?
select count(*) from reservations group by room
Which room has the largest number of reservations?
select * from reservations group by room order by count(*) desc limit 1
Tell me the name of that room.
select t2.roomname from reservations as t1 join rooms as t2 on t1.room = t2.roomid group by t1.room order by count(*) desc limit 1;