Show the total number of rooms of all apartments with facility code "Gym".
CREATE TABLE Apartments (room_count INTEGER, apt_id VARCHAR); CREATE TABLE Apartment_Facilities (apt_id VARCHAR, facility_code VARCHAR)
[SQL] SELECT SUM(T2.room_count) FROM Apartment_Facilities AS T1 JOIN Apartments AS T2 ON T1.apt_id = T2.apt_id WHERE T1.facility_code = "Gym" [/SQL]