In relational databases, what is the main function of primary keys?

The primary function of primary keys in relational databases is to uniquely identify each record in a table. This uniqueness ensures that every row in a table can be distinguished from all other rows, allowing for reliable data retrieval and integrity. By enforcing this uniqueness, primary keys prevent the occurrence of duplicate entries, which is critical for maintaining clean and accurate datasets.

In addition to identification, primary keys also contribute to the establishment of relationships between different tables within a database, often serving as a reference in foreign keys, thereby facilitating relational database operations. This role is essential for enforcing referential integrity, making data relationships clear and manageable.

The other options represent functions that do not align with the core purpose of primary keys. Storing duplicate records contradicts the primary key's principle of uniqueness. Providing user access control pertains to database security measures, and encrypting sensitive information is a data protection strategy that addresses confidentiality rather than identification.