Typical Queries for a Hotel Reservation System

Here are two typical Queries ...

Question 1 : What is the total revenue per reservation from all double rooms?

Answer 1 :
   SELECT booking_ID,SUM(room_Price*Days_in (date_To - Date_From))
   FROM   Bookings, Rooms
   WHERE  room_Type_Code LIKE 'Double%'
   AND    Bookings.room_number = Rooms.room_number
   GROUP  BY booking_ID ;

Question 2 :
How many distinct guests have made bookings for Aug. 1997 in each hotel?

Answer 2 :
    SELECT hotel_ID,hotel_Name,COUNT(DISTINCT guest_Number)
    FROM   Bookings
          ,Hotels
          ,Rooms
    WHERE ("Aug/97/" >= Month(date_From)
    OR     "Aug/97/" <= Month(date_To)  )
    AND    Bookings.room_number = Rooms.room_number
    AND    Rooms.hotel_ID       = Hotels.hotel_ID
    GROUP  BY hotel_ID, hotel_Name;