What is the role of a foreign key in a database?

The role of a foreign key in a database is to link one table to the primary key of another table. This relationship is crucial for establishing connections between different entities within the database. The foreign key effectively acts as a reference that maintains the integrity of the relationships among tables. By ensuring that the value in the foreign key matches a value in the primary key of the linked table, it allows for the enforcement of data integrity and helps prevent orphan records—or records that reference non-existent entities in the related table.

This linking facilitates various operations, such as JOINs, which allow for retrieving related data across multiple tables based on the established relationships. Using foreign keys is fundamental to maintaining a well-structured relational database, as they enable the organization of data into related categories while ensuring that relationships are logically consistent and valid.