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Use of UNIQUE while defining an attribute of a table in SQL means that the attribute values are

  • A.distinct values
  • B.cannot have NULL
  • C.both (A) & (B)
  • D.same as primary key

Answer: C

Correct answer: both (A) & (B)

In the SQL standard UNIQUE by itself permits nulls, but in the sense these questions use it - as the guarantee that the column identifies rows - it is taken to require distinct values and no nulls, which is what makes it equivalent in effect to a key.

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