NOT NULL constraints usage: For which attributes should you apply NOT NULL constraints?

NOT NULL constraints usage: For which attributes should you apply NOT NULL constraints?

• A. For optional attributes
• B. For mandatory attributes
• C. Never use NOT NULL
• D. Only on historical tables

Answer: (B)

NOT NULL is used to enforce that a value must always be present in a column. When a field is mandatory for the business rules—meaning every record must include a value for that attribute—you apply NOT NULL to ensure nothing gets left blank. This guards against incomplete data and makes the meaning of the data unambiguous, which is crucial for reliable reporting, joins, and integrity checks. Opting to allow NULL is appropriate for attributes that can legitimately be unknown or not applicable in some cases. If an attribute is optional, NULL signals that there’s no value rather than implying a misleading default. Primary keys are inherently NOT NULL because a row must have a unique, present identifier. Foreign keys can be NOT NULL if the relationship they represent is required, but not necessarily in all contexts. Applying NOT NULL only to historical tables doesn’t reflect a general rule; the decision depends on whether a value is required for every row in a given table, not on the table’s purpose.

NOT NULL is used to enforce that a value must always be present in a column. When a field is mandatory for the business rules—meaning every record must include a value for that attribute—you apply NOT NULL to ensure nothing gets left blank. This guards against incomplete data and makes the meaning of the data unambiguous, which is crucial for reliable reporting, joins, and integrity checks.

Opting to allow NULL is appropriate for attributes that can legitimately be unknown or not applicable in some cases. If an attribute is optional, NULL signals that there’s no value rather than implying a misleading default.

Primary keys are inherently NOT NULL because a row must have a unique, present identifier. Foreign keys can be NOT NULL if the relationship they represent is required, but not necessarily in all contexts.

Applying NOT NULL only to historical tables doesn’t reflect a general rule; the decision depends on whether a value is required for every row in a given table, not on the table’s purpose.