SQL中的双重否定 - NOT的含义（Food！=“Apple”）

Question

有双重否定意义的麻烦。

这些陈述是否相同？

1. NOT（Food＆lt;＆gt;“Apple”AND NOT（Food =“Banana”））

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1. （Food =“Apple”AND Food =“Banana”）

Answer 1

您正在寻找De Morgan's laws

NOT( A OR B )  = NOT A AND NOT B
NOT( A AND B ) = NOT A OR  NOT B

所以第一句应该是：

NOT (Food <> "Apple" AND NOT (Food = "Banana"))
==> NOT (Food <> "Apple" AND Food <> "Banana")       -- SOLVE inner NOT
==> NOT (Food <> "Apple") OR NOT (Food <> "Banana")  -- MORGAN LAW
==> Food = "Apple" OR Food = "Banana"                -- APPLY NOT