Which statement best describes the main purpose of a primary key?

Which statement best describes the main purpose of a primary key?

• A. Uniquely identifies each row and cannot be null.
• B. Stores auxiliary data about a row.
• C. Can be duplicated.
• D. Is always a foreign key.

Answer: (A)

The main idea is that a primary key provides a unique identity for every row in a table and must never be NULL. This guarantees that each record can be precisely distinguished and referenced, which is essential for data integrity. The values must be unique across the table, and every row must have a value for this key. It doesn’t store auxiliary data about the row—that’s the job of other columns. It cannot be duplicated. And while a primary key value can be used by other tables as a foreign key to refer to that row, the primary key itself is not necessarily a foreign key.

The main idea is that a primary key provides a unique identity for every row in a table and must never be NULL. This guarantees that each record can be precisely distinguished and referenced, which is essential for data integrity. The values must be unique across the table, and every row must have a value for this key. It doesn’t store auxiliary data about the row—that’s the job of other columns. It cannot be duplicated. And while a primary key value can be used by other tables as a foreign key to refer to that row, the primary key itself is not necessarily a foreign key.