Multiple choice technology databases

Which of the following statements are true?

  1. Primary key constraints allow NULL values in the columns.

  2. Unique key constraints allow NULL values in the columns.

  3. Primary key constraints do not allow NULL values in the columns.

  4. A nonunique index cannot be used to enforce primary key constraints.
Reveal answer Fill a bubble to check yourself
B,C Correct answer
Explanation

Unique key constraints allow NULL values, whereas primary key constraints strictly forbid NULL values in their columns. Additionally, a pre-existing non-unique index can be used to enforce a primary key constraint if created beforehand. This makes the marked true options correct and the other choices false.

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