What does a primary key define in a table?

A primary key defines a column or a combination of columns in a database table that uniquely identifies each row within that table. This unique identification is crucial because it ensures that no two rows can have the same value in that primary key column(s), which helps maintain data integrity and facilitates efficient data retrieval.

While a primary key does indeed refer to a non-duplicable value, describing it as simply a non-duplicable value does not capture the entirety of its purpose or function; it primarily serves to identify rows distinctly. The concept of a primary key also encompasses creating relationships between tables, but defining it solely in terms of relations would overlook its principal role of unique identification within a single table. Finally, the primary key is unrelated to user access types, which pertain to permissions and roles in a database system rather than data structure.