In relational databases, which statement best describes a primary key?

In relational databases, which statement best describes a primary key?

• A. The primary key must be numeric
• B. The primary key uniquely identifies each row
• C. They must be a foreign key
• D. They cannot be indexed

Answer: (B)

A primary key uniquely identifies each row in a relational table and enforces entity integrity by ensuring every record is distinct and can be reliably referenced. It cannot be NULL, and it is typically indexed to speed up lookups, which is why retrieving a row by its key is fast and efficient. A primary key does not have to be numeric; it can be a string, a composite of multiple columns, or a GUID, chosen for the best fit to the data model. Foreign keys, on the other hand, reference primary keys in other tables but are not themselves required to be, so that relationship links can be established. Also, primary keys being indexed is standard practice, so the statement that they cannot be indexed is incorrect.

A primary key uniquely identifies each row in a relational table and enforces entity integrity by ensuring every record is distinct and can be reliably referenced. It cannot be NULL, and it is typically indexed to speed up lookups, which is why retrieving a row by its key is fast and efficient. A primary key does not have to be numeric; it can be a string, a composite of multiple columns, or a GUID, chosen for the best fit to the data model. Foreign keys, on the other hand, reference primary keys in other tables but are not themselves required to be, so that relationship links can be established. Also, primary keys being indexed is standard practice, so the statement that they cannot be indexed is incorrect.