Which database concept holds a unique value identifying each record and can be composed of multiple fields?

• A. Foreign Key
• B. Index
• C. Candidate Key
• D. Primary Key

Answer: (D)

The main concept being tested is that a primary key uniquely identifies each row and can be formed from multiple fields. A primary key must have unique values for every row, and it serves as the main identifier that links records to related data in other tables. If no single column uniquely identifies a row, you can combine multiple columns to create a composite primary key that together yields a unique value for each record. For example, in a table of enrollments, the combination of student_id and course_id can act as the primary key to ensure each enrollment entry is unique. While other options relate to keys or indexing in different ways, they don’t fulfill both the guaranteed unique identification and the potential to be composed of multiple fields as clearly as the primary key.