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A UNION query is which of the following?

  • A.Combines the output from no more than two queries and must include the same number of columns.
  • B.Combines the output from no more than two queries and does not include the same number of columns.
  • C.Combines the output from multiple queries and must include the same number of columns.
  • D.Combines the output from multiple queries and does not include the same number of columns.

Answer: C

Correct answer: Combines the output from multiple queries and must include the same number of columns.

UNION stacks the result sets, so the queries must agree in the number of columns and in the types of the corresponding ones - the union compatibility requirement. There is no limit of two: any number of SELECTs may be chained with UNION.

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