The UNIQUE constraint differs from the PRIMARY KEY constraint in what way?
A) The UNIQUE constraint does not allow NULL values.
B) The UNIQUE constraint can be created at either the column level or the table level.
C) The UNIQUE constraint allows NULL values.
D) The UNIQUE constraint ensures that a specific condition is True before a data value is added to a table.

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Quizplus · Accepted Answer

The UNIQUE constraint allows NULL values, whereas the PRIMARY KEY constraint does not allow NULL values.

The UNIQUE Constraint Differs from the PRIMARY KEY Constraint in What