What is the primary purpose of a foreign key in a relational database?

The primary purpose of a foreign key in a relational database is to enforce data integrity across different tables. A foreign key is a column or a set of columns in one table that uniquely identifies a row of another table or the same table. This relationship helps maintain consistency and integrity in the database by ensuring that any value in the foreign key column corresponds to valid entries in the referenced table.

By establishing this connection, foreign keys prevent actions that would disrupt the logical relationships between data entries in different tables, such as deleting a record from a parent table that still has references in a child table. This not only preserves the integrity of the data but also helps in building relational schemas that reflect real-world relationships, making it easier to retrieve and analyze information across multiple tables.

While other options might involve maintaining or accessing the data in a database, they do not align with the specific role of a foreign key. For instance, uniquely identifying records within a single table pertains to primary keys, and storing data in a non-relational format is not relevant at all to foreign keys or relational databases. Directly manipulating data refers to operations like update and delete, which are part of data management rather than the structural integrity provided by foreign keys.