Key constraint states that:
2016
Key constraint states that:
- A.
a table can't have more than one candidate keys
- B.
a table can't have both primary key and foreign key
- C.
the value of foreign key can't be null
- D.
the value of primary key must be unique in all tuples
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Correct answer: D
a key constraint ensures that an identifier uniquely distinguishes each row within a relation. The value of a primary key must be unique in all tuples and cannot contain duplicate values, maintaining data integrity. Therefore, Option D is the correct answer.