What does the NOT ENFORCED attribute imply when adding a PRIMARY KEY constraint in a database?

• A. The database does not validate existing data against the constraint.
• B. The constraint is always enforced on insertions only.
• C. The constraint becomes a UNIQUE constraint.
• D. The constraint applies only to deletions.

Answer: (A)

Not enforcing a primary key means the database won’t validate existing rows against the constraint when you add it. This lets you declare the constraint without scanning the whole table, which is helpful for large datasets. The constraint still defines the intended rule—that each row should be uniquely identifiable by the key—but existing data may not be checked immediately. If you later decide to enforce it, many systems offer a way to validate current data and then enable enforcement for future operations. The primary key’s fundamental properties (uniqueness and not null) remain in concept, but NOT ENFORCED is about whether the system actively checks existing data right away.

The other options don’t fit because this setting doesn’t mean enforcement only during insertions, it doesn’t turn the primary key into a simple unique constraint, and it isn’t limited to deletions.