What best describes a relational database and the role of a primary key?

• A. Relational databases store data in tables with rows and columns; a primary key uniquely identifies each row.
• B. Relational databases store data as documents.
• C. Relational databases store data in graphs.
• D. Relational databases store data as key-value pairs.

Answer: (C)

Relational databases organize data into tables with rows and columns, where each table represents a type of entity. A primary key is a column (or set of columns) whose values are unique for every row, so you can identify each record unambiguously. This uniqueness is what lets you relate data across tables—through foreign keys that point to primary keys in other tables—enabling structured relationships and reliable data integrity.

Storing data as documents, graphs, or key-value pairs describes other kinds of databases: document stores hold semi-structured documents, graph databases model connections with nodes and edges, and key-value stores map a key to a value without structured relations.