WHY ARE THESE INVALID SQL QUERIES WORKING?
Posted on 2010-09-20
Hi- I'm wondering if anyone can explain to me why these functions are working correctly with the mySQL command line? They were given as examples of invalid SQL but I tested them out w/ some fake data and I'm getting correct answers.
Hotel(hotelNo, hotelName, city)
Room(roomNo, hotelNo, type, price)
Booking(hotelNo, guestNo, dateFrom, dateTo, roomNo)
Guest(guestNo, guestName, guestAddress)
CREATE VIEW HotelBookingCount(hotelNo, bookingCount) AS
SELECT h.hotelNo, COUNT(*) FROM Hotel h, Room r, Booking b
WHERE h.hotelNo=r.hotelNo AND r.roomNo=b.roomNo
GROUP BY h.hotelNo;
a) SELECT MIN(bookingCount) FROM HotelBookingCount;
should be Invalid – bookingCount is based on an aggregate function, so cannot be used within another aggregate function. (according to the textbook)
b) SELECT COUNT(*) FROM HotelBookingCount;
should be invalid for the same reason
c) SELECT hotelNo FROM HotelBookingCount WHERE bookingCount>1000;
should be Invalid – bookingCount is based on an aggregate function, so cannot be used within WHERE clause. (according to the textbook)
they all compiled & returned correct answers.