What defines a primary key in a database table?

A primary key in a database table serves the critical function of uniquely identifying each record within that table. This means that every value in the primary key must be unique — no two rows can have the same value for this field. By serving as a unique identifier, the primary key ensures data integrity and facilitates efficient data retrieval.

In most relational databases, the primary key not only guarantees uniqueness but also helps establish relationships between different tables. It acts as a reference point for foreign keys in other tables, allowing for the effective linking of data across different entities. This capability is essential for maintaining organized and coherent relationships in relational database design.

Understanding the nature of primary keys is essential for database design because they ensure that each record can be accurately identified without confusion. This uniqueness directly supports the relational model's fundamental principles, optimizing data management and retrieval processes.