Which term describes a constraint that holds a unique value identifying each record and may be composed of multiple fields?

• A. Foreign Key
• B. Candidate Key
• C. Primary Key
• D. Unique Constraint

Answer: (C)

The main idea here is identifying each row in a table with a value that is guaranteed to be unique. The term that fits is the primary key. The primary key serves as the table’s main identifier for records and enforces that no two rows share the same value. It can be a single column or a combination of multiple columns (a composite key), which is exactly when several fields together identify a row. In most databases, the primary key cannot be NULL, underscoring its role as the definitive row identity. Among the columns that could uniquely identify a row, one is chosen as the primary key. Those other potential identifiers are called candidate keys. A foreign key links to a key in another table, while a unique constraint ensures uniqueness of values within a column or set of columns but is not used as the table’s primary identifier and may allow NULLs depending on the database.