Which term describes a key field that identifies records in a table by matching a primary key in a different table?

• A. Primary Key
• B. Foreign Key
• C. Index
• D. Unique Constraint

Answer: (B)

A foreign key defines a field that identifies records in one table by matching a primary key in another table. This creates a relationship between the two tables and enforces referential integrity, meaning every value in the foreign key must exist as a primary key value in the referenced table. For example, in an orders table, a customer_id column would reference the id column in the customers table. This is what lets you link each order to the customer who placed it.

The primary key is the unique identifier for rows within its own table, not a cross-table link. An index speeds up lookups but doesn't establish a cross-table relationship. A unique constraint ensures all values in a column are distinct within the same table, not that they point to another table's key.