What is a primary key in a database?

A primary key in a database is a unique identifier for each record in a table, which is essential for ensuring data integrity and facilitating efficient data retrieval. Each value in the primary key field must be unique, meaning no two records can have the same value for that key. This uniqueness allows for precise identification of records, which is crucial in operations such as searching, updating, or deleting entries in a database.

In addition to uniqueness, a primary key also cannot contain null values, ensuring that every record is fully identifiable. This is important in maintaining the relational model of databases, where different tables can be linked through primary keys and foreign keys. The proper use of primary keys directly contributes to the robustness and reliability of a database system.