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给定关系r(R),r满足(44)函数依赖。

①A→B
②A→C
③AB→C
④C→A
⑤BC→A
⑥AC→B
A.1、2、3
B.2、3、4、5
C.3、4、5、6
D.1、2、3、6

A.shangxueba.cn/images/ct_crmsdsm_crmsdschoosecn_02294(20096).jpg'
B.1、2、3
B.2、3、4、5
C.3、4、5、6
D.1、2、3、6


【参考答案】

B
解析:①r不满足FD:A→B。因为对于元组(3,5,6)和(3,4,6),有t1(A)=3=t2(A),但是t1B)=5[*]t2(B)=4。②表中A列不等值的所有元组满足FD:A→C,称这类元组“空满足”该FD。另外,还有两个满足条件“A列等值时C列也等值”的元组,即t1(A)=3=t......

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