Multiple choice technology databases

Which of the following is used to indicate a column will not accept NULL values and can be referenced in another table's foreign key specification?

  1. Check constraint

  2. Default constraint

  3. Unique constraint

  4. Informational constraint
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C Correct answer
Explanation

A UNIQUE constraint ensures a column will not accept NULL values (in most DBMS implementations) and creates an index that can be referenced by a foreign key. CHECK constraints only validate data values, DEFAULT constraints provide fallback values, and INFORMATIONAL is not a standard constraint type.

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