What is a unique identifier for a record in a database table?

• A. Primary key
• B. Foreign key
• C. Constraints
• D. Stored locally

Answer: (A)

A primary key serves as the unique identifier for each record in a table. It guarantees that no two rows share the same key value and is typically not allowed to be null, which lets you reliably locate, update, and relate a specific row. This key is also what other tables reference with foreign keys to establish relationships. The other terms describe different ideas: a foreign key points to a primary key in another table but isn’t the table’s own unique identifier; constraints are rules that enforce data integrity (and can include primary keys, not null, unique, etc.); stored locally isn’t a concept that identifies records in a table.