What is a primary key in a relational database?

A primary key serves as a unique identifier for each row in a relational database table, ensuring that no two rows can have the same key value. This unique identification is critical for maintaining data integrity and enabling easy retrieval of records. The primary key must always contain a value, meaning it cannot be null, which reinforces its role as a reliable reference point for each entry.

Being established as the unique footprint of a row, the primary key guarantees that each record can be distinctly accessed and manipulated without confusion or ambiguity. This allows for efficient data operations, such as updates or deletions, enhancing the overall organization and structure of the data within the database.

While there are various attributes associated with primary keys—such as the prohibition of null values—what fundamentally defines them is their role in uniquely identifying records in a table, which is pivotal for relational database management.