数据库系统原理课件：作业讲评 2_4_1ppt

1、1作业讲评 2.4.1p2922.4.1 a哪些型号的PC速度大于3.00？ model( speed3.00 (PC) )32.4.1 b maker( Product hd100 (Laptop) )wrong42.4.1 b maker(type=laptop ( Product) maker (hd100 (Laptop) Product )2.4.1 c model, price (maker=B (Product PC Laptop Printer ) )wrong62.4.1 c model, price (maker=B (Product) PC ) model, price(

2、maker=B (Product) Laptop ) model, price(maker=B (Product) Printer ) 72.4.1 d model( color=true AND type=laser (Printer) )82.4.1 e maker( type=laptop (Product) ) maker( typepc (Product) )wrong92.4.1 e maker( type=laptop AND typepc (Product) ) Wrong102.4.1 e maker( type=laptop (Product) typepc (Produc

3、t) ) Wrong112.4.1 e maker( type=laptop (Product) ) maker( type=pc (Product) )122.4.1 f查询在一种或者两种PC机中出现的硬盘的容量=查询在不超过两种PC机中出现的硬盘的容量132.4.1 f查询在至少两种PC机中出现的硬盘的容量R1(model, hd):= model, hd (PC)R2(model, hd):= model, hd (PC)Answer(hd):= R1.hd ( R1 R2 ) R1.hd= R2.hd AND R1. model R2. model 142.4.1 f查询在至少3种PC

4、机中出现的硬盘的容量R1(model, hd):= model, hd (PC)R2(model, hd):= model, hd (PC)R3(model, hd):= model, hd (PC)R4(hd):= R1.hd (R1 R2 R3)R1.hd= R2.hd AND R1. model R2. model R2.hd= R3.hd AND R2. model R3. modelWrong 非传递关系 考虑 R1=R3 R2 152.4.1 f查询在至少3种PC机中出现的硬盘的容量R1(model, hd):= model, hd (PC)R2(model, hd):= mode

5、l, hd (PC)R3(model, hd):= model, hd (PC)R4(hd):= R1.hd (R1 R2 R3)R1.hd= R2.hd AND R1. modelR2. model R2.hd= R3.hd AND R2. modelR3. model162.4.1 f查询在不超过两种PC机中出现的硬盘的容量Answer(hd):= hd (PC) R4172.4.1 gR1(model, speed,ram):= model, speed, ram (PC)R2(model, speed,ram):= model, speed, ram (PC)Answer(R1.mod

6、el, R2.model):= R1.model, R2.model ( R1 R2) R1. speed = R2. speed AND R1. ram = R2. ram AND R1. model 2.8 (PC) product ) maker, model(speed2.8 (Laptop) product )R2:=R1Answer(maker):= R1.maker (R1 R2) R1. maker = R2. maker AND R1. model R2. Model192.4.1 jR1(maker, speed):= maker, speed ( PC product )

7、 maker, speed ( Laptop product )R2:=R1 R3:=R1Answer(maker):= R1.maker(R1 R2 R3)R1. maker=R2.maker AND R1.speedR2. speed R2.maker=R3.maker AND R2.speedR3.speed202.4.1k至少生产3种型号PC的厂商R1(maker, model):= maker, model (type=PC ( Product) )R2:=R1, R3:=R1, R4:=R1R5 (maker):= R1. maker(R1 R2 R3)R1. maker = R2. maker AND R1. model R2. model R2.maker=R3.maker AND R2.modelR3. model212.4.1k 续至少生产4种型号PC的厂商R6 (maker):= R1. maker(R1 R2 R3 R4)R1.maker=R2.maker AND R1.modelR2