What role does a foreign key play in a relational database?

A foreign key serves a crucial function in a relational database by establishing and enforcing a relationship between two tables. It is a column (or a set of columns) in one table that refers to the primary key in another table. This connection allows for data integrity and supports the relational model by enabling the combination of related data across different tables.

For example, consider a scenario with two tables: one for customers and another for orders. The customer table might have a primary key, such as CustomerID, which uniquely identifies each customer. The orders table would then include a foreign key that references the CustomerID from the customer table. This relationship allows users to query data across both tables effectively, ensuring that every order corresponds to an existing customer.

Through this mechanism, foreign keys help maintain referential integrity, meaning that relationships between tables remain consistent. If a record in the primary table is deleted or altered, the database can enforce rules to prevent orphaned records in the related table.

This accurate linkage set by foreign keys also simplifies complex queries, enabling developers to join tables based on those relationships effortlessly. Hence, the role of a foreign key in a relational database is paramount for maintaining structured data and enabling relational operations efficiently.