Explain what is meant by a ForeignKey relationship in a database and how it functions.

ForeignKey — a relationship between tables in a relational database that ensures referential integrity. It indicates that the value in one column (or set of columns) in one table corresponds to the primary key value in another table.

For example, there is an Orders table with a customer_id field, which is a foreign key referencing the id field in the Customers table. This means each order is linked to a specific customer.

Functioning:

• Foreign key values must exist in the related table (or be NULL if allowed).
• When deleting or updating a record in the parent table, cascade actions can be configured (e.g., delete related records).

This helps maintain data integrity and simplifies working with related tables.