CREATE TABLE dorm_amenity (amenid DECIMAL, amenity_name TEXT)
CREATE TABLE lives_in (stuid DECIMAL, dormid DECIMAL, room_number DECIMAL)
CREATE TABLE dorm (dormid DECIMAL, dorm_name TEXT, student_capacity DECIMAL, gender TEXT)
CREATE TABLE has_amenity (dormid DECIMAL, amenid DECIMAL)
CREATE TABLE student (stuid DECIMAL, lname TEXT, fname TEXT, age DECIMAL, sex TEXT, major DECIMAL, advisor DECIMAL, city_code TEXT)

Find the name of amenity that is most common 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
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 NULLS LAST LIMIT 1