A null value is assigned when no other value applies.

More Questions from Logical Database Design

• A candidate key must uniquely identify each row.
• A composite attribute does not get mapped into a relation.
• A synonym is two or more attributes that have different names but the same meaning.
• If a relation is in third normal form, it does not need to be in second normal form.
• Well-structured relations encourage anomalies of data.
• A foreign key may be null and still adhere to the referential integrity constraint.
• The primary key in a relation does not need to be underlined.

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