What is the apartment type code for "Suite 643"?
SELECT T2.apt_type_code FROM Apartment_Bookings AS T1 JOIN Apartments AS T2 ON T1.apt_id   =   T2.apt_id WHERE T2.apt_number   =   "Suite 634"
apartment type code refers to apt_type_code; 'Suite 643' is specified by apt_number = 'Suite 643'; JOIN is used to connect Apartment_Bookings and Apartments tables on apt_id.