What is a primary key in a relational database?

A primary key in a relational database is defined as a unique identifier for a record in a table. This means that each entry in a table can be distinctly recognized using the primary key, ensuring that there are no duplicate records. The primary key plays a crucial role in maintaining the integrity and consistency of the data within the database. It ensures that each record can be referenced accurately, which is essential for performing operations such as querying, updating, and deleting records.

This unique identifier is critical because it allows relationships to be established between different tables in the database. When a primary key is used in one table, it can be referenced as a foreign key in another table, reinforcing the connections between related data across different entities. The primary key’s uniqueness directly impacts the database's ability to efficiently query information and maintain data integrity throughout.

The other options describe characteristics that are not aligned with the definition of a primary key. For example, a key that allows multiple entries in a table does not serve the purpose of uniquely identifying records; rather, that would indicate a lack of uniqueness. Similarly, while a foreign key does relate to another table, it does not serve as a primary identifier within the table where it exists. Lastly, a key that enforces data redundancy contradicts