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Which is NOT one of the most common types of SQL CHECK constraints?

  • A.System date
  • B.Range checks
  • C.Lists of values
  • D.
    Comparing one column value to another within the same table

Answer: A

Correct answer: System date

The three common forms are range checks, lists of permitted values, and comparisons between two columns of the same row. Comparing against the system date is not among them and is in fact problematic, since the condition would be evaluated afresh on every check and a row valid when inserted could become invalid with the passage of time.

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