Some functional dependencies: if X and Y, but not fully function depends on the X, Y, said part of X Y function dependence,
Function depends on the K if U parts, namely, the K - P U K called super size,
Baidu encyclopedia,,
Super size, it is to point to a collection of one or more attributes,
(Sno, Cno, for example) to U Sno, U know U part function depends on (Sno, Cno), the smallest super size for attributes columns Sno (i.e., the candidate code),
And so the question becomes, Sno U.U function completely dependent on Sno, isn't it, why can Sno attribute column called super size
