2.4.14 Exercises for Section 2.4 Exercise 2.4.1: This exercise builds upon the products schema of Exercise 2.3.1. Recall that the database schema consists of four relations, whose schemas are:
2.4.14 Exercises for Section 2.4 Exercise 2.4.1: This exercise builds upon the products schema of Exercise 2.3.1. Recall that the database schema consists of four relations, whose schemas are:
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Transcribed Image Text:2.4.14 Exercises for Section 2.4
Exercise 2.4.1: This exercise builds upon the products schema of Exercise
2.3.1. Recall that the database schema consists of four relations, whose schemas
are:
Product (maker, model, type)
PC (model, speed, ram, hd, price)
Laptop (model, speed, ram, hd, screen, price)
Printer (model, color, type, price)
Some sample data for the relation Product is shown in Fig. 2.20. Sample
data for the other three relations is shown in Fig. 2.21. Manufacturers and
model numbers have been "sanitized," but the data is typical of products on
sale at the beginning of 2007.
Write expressions of relational algebra to answer the following queries. You
may use the linear notation of Section 2.4.13 if you wish. For the data of Figs.
2.20 and 2.21, show the result of your query. However, your answer should work
for arbitrary data, not just the data of these figures.
a) What PC models have a speed of at least 3.00?
b) Which manufacturers make laptops with a hard disk of at least 100GB?
c) Find the model number and price of all products (of any type) made by
manufacturer B.
d) Find the model numbers of all color laser printers.
e) Find those manufacturers that sell Laptops, but not PC's.
! f) Find those hard-disk sizes that occur in two or more PC's.
2.4. AN ALGEBRAIC QUERY LANGUAGE
maker model type
1001 рс
1002 pc.
1003 pc
A
A
A
A
A
A
B
B
B
B
с
D
D
D
D
D
E
E
E
E
E
E
E
E
E
F
F
G
H
H
2004 laptop
2005 laptop
laptop
2006
1004
рс
1005 рс
1006 pc
2007 laptop
1007 рс
pc.
pc
рс
1008
1009
1010
3004 printer
3005
printer
1011
pc
1012 pc
pc
1013
2001 laptop
2002
laptop
2003
laptop
3001
printer
3002 printer
3003 printer
2008 laptop
2009
laptop
2010 laptop
3006 printer
3007 printer
Figure 2.20: Sample data for Product
53
Transcribed Image Text:54
CHAPTER 2. THE RELATIONAL MODEL OF DATA
model speed ram | hd
hd
price
1001 2.66 1024 250 2114
1002 2.10
512 250
995
512 80
478
1003 1.42
1004 2.80 1024 250
649
1005 3.20 512 250
630
1006 3.20 1024 320
1049
510
1007 2.20 1024 200
1008 2.20
2048 250
1009 2.00 1024 250
770
650
1010 2.80 2048 300
770
959
1011 1.86 2048 160
1012 2.80 1024 160 649
1013 3.06 512 80 529
(a) Sample data for relation PC
model speed ram hd screen
price
2001 2.00 2048 240 20.1 3673
2002 1.73 1024 80
17.0
949
549
1150
2003 1.80 512 60 15.4
2004 2.00 512 60 13.3
2005 2.16
1024 120 17.0
2006 2.00 2048 80 15.4
2500
1700
2007
1429
1.83
1024 120 13.3
1.60 1024 100 15.4
2008
900
680
2009 1.60 512 80 14.1
2010 2.00 2048 160 15.4 2300
(b) Sample data for relation Laptop
model color type
3001 true ink-jet
3002 false
laser
laser
price
99
239
899
120
120
100
200
3003 true
3004 true
3005 false laser
3006 true
ink-jet
3007 true laser
(c) Sample data for relation Printer
Figure 2.21: Sample data for relations of Exercise 2.4.1
ink-jet
2.4. AN ALGEBRAIC QUERY LANGUAGE
! g) Find those pairs of PC modeis that have both the same speed and RAM.
A pair should be listed only once; e.g., list (i, j) but not (j, i).
55
!! h) Find those manufacturers of at least two different computers (PC's or
laptops) with speeds of at least 2.80.
!! i) Find the manufacturer(s) of the computer (PC or laptop) with the highest
available speed.
!! j)
Find the manufacturers of PC's with at least three different speeds.
!! k) Find the manufacturers who sell exactly three different models of PC.
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