23.17 Using the Hotel schema given at the start of the Exercises at the end of C

Question

23.17 Using the Hotel schema given at the start of the Exercises at the end of Chapter 4, determine whether the following queries are semantically correct:

(a)

SELECT r.type, r.price

FROM Room r, Hotel h

WHERE r.hotel_number = h.hotel_number AND h.hotel_name = ‘Grosvenor Hotel’ AND r.type > 100;

(b)

SELECT g.guestNo, g.name

FROM Hotel h, Booking b, Guest g

WHERE h.hotelNo = b.hotelNo AND h.hotelName = ‘Grosvenor Hotel’;

(c)

SELECT r.roomNo, h.hotelNo

FROM Hotel h, Booking b, Room r

WHERE h.hotelNo = b.hotelNo AND h.hotelNo = ‘H21’ AND b.roomNo = r.roomNo AND type = ‘S’

      AND b.hotelNo = ‘H22’;

Explanation / Answer

a)

Not semantically correct :

hotel_number and hotel_name are not the names of attributes in the schema;type is character string and so cannot be compared with an integer value(100).

b)Not semantically correct :

g.name and h.hName not in schema;guest table not connected to remainder of query.

c)Not semantically correct :

hotelNo cannot be both H21 in hotel and h22 in booking

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