定義: 在Y函數依賴於X函數的基礎上,即X→YX\to YX→Y時,如果Y⊂XY \subset XY⊂X,那麼稱X→YX\to YX→Y是平凡的函數依賴,
如果有Y⊂XY \subset XY⊂X,那麼X→YX\to YX→Y一定成立
原因:因爲Y⊂XY \subset XY⊂X,那麼Y必然是X中的一部分,因爲X確定了,那麼自然其子集也確定了,整體可以決定部分
整體可以決定部分
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