Find the decor of each room
select decor from rooms
For each type of decor, how many reservations were made?
select count(t2.decor) from reservations as t1 join rooms as t2 on t1.room = t2.roomid group by t2.decor
Which decor is the least popular?
select t2.decor from reservations as t1 join rooms as t2 on t1.room = t2.roomid group by t2.decor order by count(t2.decor) asc limit 1;