《数据库系统原理教学》作业讲评(2)ppt课件

1、作业讲评作业讲评 2.4.1p29l哪些型号的哪些型号的PC速度大于速度大于3.00？l model( speed3.00 (PC) )l maker( Product hd100 (Laptop) )lwrongl maker(type=laptop ( Product) l maker (hd100 (Laptop) Product )l model, price (l(maker=B (Product PC Laptop Printer ) l)lwrongl model, price (maker=B (Product) PC ) l l model, price(maker=B (P

2、roduct) Laptop ) l l model, price(maker=B (Product) Printer ) l model( color=true AND type=laser (Printer) )l maker( type=laptop (Product) ) l maker( typepc (Product) )lwrongl maker( type=laptop AND typepc (Product) ) lWrongl maker( ltype=laptop (Product) typepc (Product) l) lWrongl maker( type=lapt

3、op (Product) ) l maker( type=pc (Product) )l查询在一种或者两种查询在一种或者两种PC机中出现的硬盘机中出现的硬盘的容量的容量l=l查询在不超越两种查询在不超越两种PC机中出现的硬盘的机中出现的硬盘的容量容量l查询在至少两种查询在至少两种PC机中出现的硬盘的容量机中出现的硬盘的容量lR1(model, hd):= model, hd (PC)lR2(model, hd):= model, hd (PC)lAnswer(hd):= R1.hd ( R1 R2 )l R1.hd= R2.hd AND R1. model R2. model l查询在至少查询

4、在至少3种种PC机中出现的硬盘的容量机中出现的硬盘的容量lR1(model, hd):= model, hd (PC)lR2(model, hd):= model, hd (PC)lR3(model, hd):= model, hd (PC)lR4(hd):= l R1.hd (R1 R2 R3)lR1.hd= R2.hd AND R1. model R2. model l R2.hd= R3.hd AND R2. model R3. modellWrong 非传送关系非传送关系 思索思索 R1=R3 R2 l查询在至少查询在至少3种种PC机中出现的硬盘的容量机中出现的硬盘的容量lR1(mod

5、el, hd):= model, hd (PC)lR2(model, hd):= model, hd (PC)lR3(model, hd):= model, hd (PC)lR4(hd):= l R1.hd (R1 R2 R3)lR1.hd= R2.hd AND R1. modelR2. model l R2.hd= R3.hd AND R2. modelR3. modell查询在不超越两种查询在不超越两种PC机中出现的硬盘的容量机中出现的硬盘的容量lAnswer(hd):= hd (PC) R4lR1(model, speed,ram):= model, speed, ram (PC)lR2

6、(model, speed,ram):= model, speed, ram (PC)lAnswer(R1.model, R2.model):= l R1.model, R2.model ( R1 R2)l R1. speed = R2. speed AND R1. ram = R2. ram l AND R1. model 2.8 (PC) product ) l maker, model(speed2.8 (Laptop) product )lR2:=R1lAnswer(maker):= R1.maker (R1 R2)l R1. maker = R2. maker AND R1. mod

7、el R2. ModellR1(maker, speed):=l maker, speed ( PC product ) l maker, speed ( Laptop product )lR2:=R1 lR3:=R1lAnswer(maker):= l R1.maker(R1 R2 R3)lR1. maker=R2.maker AND R1.speedR2. speed l R2.maker=R3.maker AND R2.speedR3.speedl至少消费至少消费3种型号种型号PC的厂商的厂商lR1(maker, model):=l maker, model (type=PC ( Product) )lR2:=R1, R3:=R1, R4:=R1lR5 (maker):=l R1. maker(R1 R2 R3)lR1. maker = R2. maker AND R1. model R2. model l R2.maker=R3.maker AND R2.modelR3. modell至少消费至少消费4种型号种型号PC的厂商的厂商lR6 (maker):=l R1. maker(R1 R2 R3 R4)lR1.maker=R2.maker AND R1.modelR2.model l R2