What is the main purpose of a foreign key?

The primary purpose of a foreign key in a relational database is to maintain referential integrity between tables. A foreign key acts as a link between records in different tables, ensuring that the relationship between these tables remains consistent. Specifically, it establishes a constraint that enforces the existence of a corresponding primary key in another table; thus, every value in the foreign key must match a value in the referenced primary key or remain null if allowed.

By enforcing this rule, the foreign key helps prevent orphaned records and ensures that relationships between tables accurately reflect the underlying data model. Maintaining referential integrity is crucial for ensuring data accuracy and consistency across the database, allowing for reliable queries and data manipulation.

While speeding up data retrieval and managing data growth are important considerations in database design, they are not the primary functions of a foreign key. Similarly, encrypting database connections relates to security rather than the structural integrity of the data itself. Hence, the focus on referential integrity clarifies the core purpose of foreign keys in relational database models.