Which term denotes a limitation on the data entered within a data field in a database?

• A. Constraint
• B. Concurrency
• C. Class
• D. Clone

Answer: (A)

The main idea is enforcing data validity through constraints. A constraint is a rule applied to a column or table that limits what data can be stored, helping ensure data accuracy and consistency. Examples include requiring a value (NOT NULL), preventing duplicates (UNIQUE), ensuring a value meets a condition (CHECK), or enforcing valid references to another table (FOREIGN KEY). Because constraints actively restrict which data values are permitted, they are exactly the mechanism used to limit what can be entered in a data field.

Other terms don’t describe this control over input: concurrency relates to multiple operations happening at the same time, a class is a blueprint in object‑oriented design, and a clone is an exact copy.