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我有一个关系 R(A,B,C,D,E,G,H) ,其功能依赖关系:
AB -> CD
E -> D
ABC -> DE
E -> AB
D -> AG
ACD -> BE
H 不依赖于任何东西,但它不在依赖项中。
我的问题是 {HE} 是候选键{HE}+ = R吗?
{HE}+ = R
或者
E 是候选键,因为{E}+ = R
{E}+ = R
{CDH}{HE}{ABH}{BDH}
是候选键。所以确实,HE是Candidate Key,但不是唯一决定洞关系的人。看到函数依赖是第一范式(1NF)