What describes the function of a foreign key in Azure SQL Database?

The function of a foreign key in Azure SQL Database is primarily to link tables together to enforce referential integrity. A foreign key is a column or a group of columns in one table that uniquely identifies a row of another table or the same table. By using foreign keys, you create a relationship between two tables, which helps maintain consistent and valid data throughout the database. This relationship ensures that the data remains accurate and reliable, preventing orphaned records and allowing for proper data validation.

For instance, if you have a "Customers" table and an "Orders" table, the foreign key in the "Orders" table that refers to the "Customers" table ensures that every order is linked to a valid customer. This not only enforces that orders cannot exist without a corresponding customer but also allows for complex queries and data manipulation, ensuring that referential integrity is maintained when data is altered or deleted.

The other options do not accurately describe the primary role of a foreign key. While it's true that certain indexing strategies related to keys may impact performance, speeding up data retrieval is not the primary function. A unique identifier for a database is typically fulfilled by primary keys, not foreign keys. Defining user permissions is a separate aspect of database security and management, unrelated to