In a relational database, what does a foreign key represent?

A foreign key in a relational database serves as a reference to a primary key in another table. This relationship facilitates the connection between two tables, allowing data in one table to correspond with data in another. Specifically, the foreign key establishes a link that enables the database to maintain data integrity and enforce referential integrity constraints.

For instance, if you have an “Orders” table and a “Customers” table, the “CustomerID” in the “Orders” table can serve as a foreign key that relates to the “CustomerID” primary key in the “Customers” table. This setup ensures that each order is associated with a valid customer, thus maintaining the logical relationships within the database.

The other options do not accurately describe the function of a foreign key. A primary key in the same table refers to the unique identifier within that specific table, which is distinct from foreign key relationships. Storing multiple data types in a single field contradicts database normalization principles, where each column ideally contains a single type of data. Additionally, a redundant copy of primary data would violate the efficiency principles of database design, as foreign keys are meant to reference rather than duplicate information.