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What is the difference between UNION and UNION ALL?

  1. A UNION removes duplicate rows; UNION ALL keeps them and is faster
  2. B UNION ALL removes duplicates
  3. C UNION joins tables horizontally
  4. D They are identical
Answer

UNION removes duplicate rows; UNION ALL keeps them and is faster

Deduplication requires sorting or hashing, so UNION ALL should be preferred whenever duplicates are impossible or acceptable.

All Data MCQs

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