What is the primary purpose of a primary key in a relational database?

What is the primary purpose of a primary key in a relational database?

• A. Link two tables
• B. Unique identifier for a given record
• C. Store data
• D. Enforce security

Answer: (B)

The main idea is that a primary key uniquely identifies every row in a relational table. It ensures entity integrity by preventing duplicates and disallowing nulls for that key, so each record can be precisely distinguished. This unique identifier also serves as the anchor for relationships with other tables through foreign keys, enabling reliable joins and cross-table references. Data is stored in other columns of the table, and security is handled through permissions—not by the key itself. While a primary key can be referenced by foreign keys to link tables, its essential purpose is to provide a stable, unique identity for each record.

The main idea is that a primary key uniquely identifies every row in a relational table. It ensures entity integrity by preventing duplicates and disallowing nulls for that key, so each record can be precisely distinguished. This unique identifier also serves as the anchor for relationships with other tables through foreign keys, enabling reliable joins and cross-table references. Data is stored in other columns of the table, and security is handled through permissions—not by the key itself. While a primary key can be referenced by foreign keys to link tables, its essential purpose is to provide a stable, unique identity for each record.