複選題
40、Which of the following descriptions about foreign key are not correct?
(A) Foreign key must refer to the primary key of other relation.
(B) Foreign key is not necessary a primary key in its own relation.
(C) Foreign key must have the same name as the primary key it refers to.
(D) Foreign key cannot have null value.

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統計： A(4), B(8), C(11), D(8), E(0) #872819