Em có 4 bảng như sau:
1/ Province: ProvinceID, Province_name, Postal_code
2/ Hotel_info: Province_name, HotelID, Hotel_name, Hotel_class, Add, Tel, Fax
3/ Contract: ContractID, HotelID, Signed_date, Expired_date
4/ Room_rate: RoomID, ContractID, Rate
Em muốn tạo ra 1 sub query chỉ...