Multiple choice technology programming languages

Which statements are true about constraints?

  1. The UNIQUE constraint does not permit a null value for the column.

  2. The PRIMARY KEY and FOREIGN KEY constraints create a UNIQUE index.

  3. The NOT NULL constraint ensures that null values are not permitted for the column.

  4. A UNIQUE index gets created for columns with PRIMARY KEY and UNIQUE constraints.
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A,C Correct answer
Explanation

The UNIQUE constraint allows null values (unless combined with NOT NULL). A UNIQUE index is automatically created for columns defined with PRIMARY KEY and UNIQUE constraints, making that statement correct, while NOT NULL ensures no nulls are allowed.

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