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Which of the following is TRUE about UNIQUE constraint?

8. Which of the following is TRUE about UNIQUE constraint?

1. In columns that are subject to the UNIQUE constraint, duplicate values are not allowed.
2. Unique values will always be present in the column containing the unique constraint.
3. A single table can have more than one unique constraint, since it can be applied to more than one column.
4. All of the above

Answer: D) All of the above

Explanation:

In case of UNIQUE constraint:

1. In columns that are subject to the UNIQUE constraint, duplicate values are not allowed.
2. Unique values will always be present in the column containing the unique constraint.
3. A single table can have more than one unique constraint, since it can be applied to more than one column.