In relational databases, a foreign key is best described as?

• A. A field that uniquely identifies a row within the same table.
• B. A field used to enforce a one-way permission policy.
• C. A field in a table used to create a relationship to another table.
• D. A field that stores large binary objects.

Answer: (C)

In relational databases, a foreign key creates a link between two tables by referencing a key in another table. This is how relationships are modeled: a column (or set of columns) in one table points to the primary key (or another unique key) in a different table, establishing referential integrity. For example, an Orders table might have a CustomerID that references Customers.CustomerID. This ensures every order is associated with a valid customer, and you can join the tables to pull related data.

A foreign key does not have to be unique within its table—many rows in the child table can reference the same parent row, enabling one-to-many relationships. It is different from a primary key, which uniquely identifies rows within its own table. And it’s not about permissions or storing large binary data; those correspond to other concepts.