If I have a schema say R={A,B,C,D} and functional dependencies say {B->C, D->A} will my set of candidate keys be {B,D} or {BD}?
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Sean
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Is this homework? If so then please tag it as such. – Paul Sasik Sep 28 '11 at 22:55
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Yes, part of a question. I've answered it using {BD} but am having second thoughts – Sean Sep 28 '11 at 23:12
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What do you think the difference is between {B,D} and {BD} ???? – Erwin Smout Sep 29 '11 at 14:52
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{BD} means that you need B AND D, where {B,D} means you need B OR D – Sean Sep 30 '11 at 02:24
1 Answers
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If B were a candidate key, you'd have to be able to derive these functional dependencies from the ones given in the problem.
- {B->A}
- {B->C}
- {B->D}
Can you do that?
Mike Sherrill 'Cat Recall'
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