《数据库系统原理教学课件》作业讲评.pptx

1作业讲评p29

2.4.1a2?model(бspeed3.00(PC))哪些型号的PC速度大于3.00？

32.4.1b?maker(Productбhd100(Laptop))wrong

b?maker(бtype=‘laptop’(Product))–?maker(бhd100(Laptop)Product)12

?model,price((бmaker=‘B’(ProductPCLaptopPrinter))wrong32142.4.1c

2.4.1c60504020301?model,price(бmaker=‘B’(Product)PC)??model,price(бmaker=‘B’(Product)Laptop)??model,price(бmaker=‘B’(Product)Printer)

2.4.1d7?model(бcolor=‘true’ANDtype=‘laser’(Printer))

2.4.1e81?maker(бtype=‘laptop’(Product))–2?maker(бtype‘pc’(Product))3wrong

2.4.1e9?maker(бtype=‘laptop’ANDtype‘pc’(Product))Wrong12

2.4.1e10STEP4STEP3STEP2STEP1?maker(бtype=‘laptop’(Product)?бtype‘pc’(Product))Wrong

2.4.1e11?maker(бtype=‘laptop’(Product))–01?maker(бtype=‘pc’(Product))02

2.4.1f121查询在一种或者两种PC机中出现的硬盘的容量2=3查询在不超过两种PC机中出现的硬盘的容量

2.4.1f1323145R1.hd=R2.hdANDR1.modelR2.modelAnswer(hd):=?R1.hd(R1R2)R1(model,hd):=?model,hd(PC)R2(model,hd):=?model,hd(PC)查询在至少两种PC机中出现的硬盘的容量

2.4.1f14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):=?model,hd(PC)R3(model,hd):=?model,hd(PC)R4(hd):=?R1.hd(R1R2R3)R1.hd=R2.hdANDR1.modelR2.modelR2.hd=R3.hdANDR2.modelR3.modelWrong非传递关系考虑R1=R3R2

2.4.1f15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):=?model,hd(PC)R3(model,hd):=?model,hd(PC)R4(hd):=?R1.hd(R1R2R3)R1.hd=R2.hdANDR1.modelR2.modelR2.hd=R3.hdANDR2.modelR3.model

2.4.1f16logo查询在不超过两种PC机中出现的硬盘的容量Answer(hd):=?hd(PC)–R4

2.4.1g17R1(model,speed,ram):=?model,speed,ram(PC)R2(model,speed,ram):=?model,speed,ram(PC)Answer(R1.model,R2.model):=?R1.model,R2.model(R1R2)R1.speed=R2.speed