First, a functional dependency in the form A->B means that, given one value for A, we can determine one and only one value for B. Both A and B represent sets of columns. (That‘s why they‘re written in uppercase letters.)
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First, a functional dependency in the form A->B means that, given one value for A, we can determine one and only one value for B. Both A and B represent sets of columns. (That‘s why they‘re written in uppercase letters.) |
原文：http://www.cnblogs.com/aomi/p/7676360.html