A Level Computer Science OCR Practice Exam

What does a foreign key represent in a database?

1. A key that defines the relationship within the same table

2. A linking field in a foreign table that relates to a primary key

3. A unique identifier for all records

4. An optional field in the table

The correct answer is: A linking field in a foreign table that relates to a primary key

A foreign key serves a critical role in relational databases by establishing a relationship between two tables. Specifically, it is a linking field in one table (often referred to as the foreign table) that references the primary key of another table. This relationship is essential for maintaining referential integrity, ensuring that the data across the tables remains consistent. For instance, if one table contains customer details and another contains orders, the foreign key in the orders table might reference the customer ID from the customers table, creating a direct link between the two sets of data. This setup allows for efficient data retrieval and organization within the database. The other options do not accurately describe a foreign key. The first option pertains more to a primary key within the same table, while the third mentions a unique identifier, which describes a primary key rather than a foreign key. The last option refers to the optional nature of fields in a database schema, which does not capture the functional essence of a foreign key.