What distinguishes a primary key from a foreign key in databases?

A primary key and a foreign key serve distinct purposes in the context of database design and management. The primary key is a unique identifier for a record within its own table, ensuring that each entry can be distinctly referenced without ambiguity. By definition, a primary key must contain unique values, and it cannot be null, which guarantees that every record is accessible based on this unique identifier.

The foreign key, on the other hand, is used to establish a relationship between two tables. It is a field (or a collection of fields) in one table that uniquely identifies a row of another table, thereby linking the two tables together. This linkage allows for the enforcement of referential integrity within the database, meaning that the foreign key values must correspond to existing primary key values in the referenced table.

In summary, the statement that distinguishes a primary key from a foreign key accurately reflects their roles: the primary key identifies each record uniquely within a table, while the foreign key acts as a bridge linking records across different tables. This connection is fundamental to relational database design, facilitating the organization and retrieval of data across multiple entities.