How many amenities are offered in all dorms?
select count ( * ) from dorm_amenity
Could you tell me the names of these amenities?
select amenity_name from dorm_amenity
What is the name of the most common amenity in all dorms?
select t1.amenity_name from dorm_amenity as t1 join has_amenity as t2 on t1.amenid = t2.amenid group by t2.amenid order by count ( * ) desc limit 1