上海交通大学：《数据库系统原理 The principle of Database System》教学资源_第二章习题与答案（第三版）

Exercise 2.4.1 a),f),h) Product(maker,model,type) PC(model,speed,ram,hd,price) Laptop(model,speed,ram,hd,screen,price) Printer(model,color,type,price) Write expressions of relational algebra to answer the following queries.For the data of Figs2.20 and 2.21,show the result of your query a)what PC models have a speed of at least 3.00? t Mode (o(speed >=3.00)(PC)) Result: 1005 1006 1013 f)Find those hard-disk sizes that occur in two or more PC's. R1=Ppel (PC) R2=Ppe2(PC) R3=R1 0-JOIN (pe1.hd=pe2.hd and pel.model pe2.model)R2 R4=元pc1hd(R3) Result: 250 80 160 h)Find those manufacturers of at least two different computers(PC's or laptops)with speeds of at least 2.8 R1=Tmodel.speed(PC)modelspeed (Laptop) R2=TMakermodel ((speed>=28(R1)natural JOIN Product)) R3=p T(maker2,model2)(R2) R4=R2 theta JOIN maker=maker2 AND modelmodel2(R3) Answer(maker)=Maker (R4) Result: B,E Exercise 2.5.1 b) Product(maker,model,type) PC(model,speed,ram,hd,rd,price) Laptop(model,speed,ram,hd,screen,price) Printer(model,color,type,price) Write your constraints either as containments or by equating an expression to the empty set.For

Exercise 2.4.1 a), f), h) Product (maker, model, type) PC(model, speed, ram, hd, price) Laptop(model,speed,ram,hd,screen,price) Printer(model,color,type,price) Write expressions of relational algebra to answer the following queries. For the data of Figs2.20 and 2.21, show the result of your query. a) what PC models have a speed of at least 3.00？  Model ( (speed >=3.00) (PC)) Result: 1005 1006 1013 f) Find those hard-disk sizes that occur in two or more PC’s. R1 = pc1 (PC) R2 = pc2 (PC) R3 = R1 -JOIN (pc1.hd = pc2.hd and pc1.model <>pc2.model) R2 R4 =  pc1.hd (R3) Result: 250 80 160 h) Find those manufacturers of at least two different computers (PC’s or laptops) with speeds of at least 2.8 R1 = model,speed (PC)   model,speed (Laptop) R2 = Maker,model ( (Speed >= 2.8 (R1) natural JOIN Product)) R3 =  T(maker2,model2)(R2) R4 = R2 theta JOIN maker=maker2 AND model <> model2 (R3) Answer(maker) = Maker (R4) Result: B,E Exercise 2.5.1 b) Product (maker, model, type) PC(model, speed,ram,hd,rd,price) Laptop(model,speed,ram,hd,screen,price) Printer(model,color,type,price) Write your constraints either as containments or by equating an expression to the empty set. For

the data of exercise 2.4.1,indicate any violations to your constraints. b)A laptop with a screen size less than 15.4 inches must have at least a 100 gigabyte hard disk or sell for less than $1000 Gsereen$1000(Laptop)= Or: Gscreen=100OR price<1000 (Laptop) Violation Model speed ram hd screen price 20042.005126013.31150

the data of exercise 2.4.1, indicate any violations to your constraints. b) A laptop with a screen size less than 15.4 inches must have at least a 100 gigabyte hard disk or sell for less than $1000 screen = $1000 (Laptop) =  Or: screen = 100 OR price < &1000 (Laptop) Violation: Model speed ram hd screen price 2004 2.00 512 60 13.3 1150