複選題
41、Which of the following descriptions about key are not correct?
(A) Primary key must be a composite key and cannot be a simple key.
(B) Superkey, candidate key and primary key can all uniquely identify any given entity (row).
(C) Primary key is not a minimal superkey.
(D) There might be more than one candidate key in a relation.

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統計： A(13), B(5), C(9), D(5), E(0) #872820