Which of the following are key fields in a relational database?

• A. Primary key
• B. Foreign key
• C. Both primary and foreign keys
• D. Neither

Answer: (C)

In a relational database, keys come in to two essential roles: identifying records and linking tables. The primary key uniquely identifies each row within its own table, ensuring every record can be found and distinguished. The foreign key, on the other hand, is a field (or set of fields) in one table that points to the primary key in another table. This creates a relationship between the two tables and enforces referential integrity, so related data across tables stays consistent. While a foreign key can contain duplicates and may be null in some designs, it is still a key field because it enables the relational structure between tables. Together, both primary keys and foreign keys are fundamental key fields in relational databases.