In a relational database, which key uniquely identifies

Solution

A Primary Key uniquely identifies each record (or tuple) in a table and cannot contain NULL values. It enforces entity integrity, ensuring that every row in a table has a unique identifier. For example, in a table of employees, an employee ID serves as a primary key, ensuring no duplicate or NULL entries exist. Why Other Options Are Incorrect:

• Foreign Key: Links one table to another and can contain NULL values in some cases; its purpose is to enforce referential integrity, not uniqueness within its table.
• Candidate Key: A potential key that can uniquely identify tuples but is not chosen as the primary key.
• Alternate Key: A candidate key not selected as the primary key but still capable of uniquely identifying records.
• Composite Key: A primary key consisting of multiple columns but is a type of primary key, not a separate concept.