Which statement best describes the relationship between candidate keys and the primary key?

• A. Candidate keys are all minimal attribute sets that could uniquely identify a row.
• B. Candidate keys are always the primary key.
• C. Candidate keys cannot be used for identification.
• D. Candidate keys include every attribute in the table.

Answer: (A)

Candidate keys are the minimal sets of attributes that can uniquely identify a row, and minimal means no subset of that set can still uniquely identify. This is why they’re described as potential primary keys: each candidate key could serve as the table’s main identifier, and the primary key is simply one chosen from among these candidate keys to act as the official unique identifier. So the statement that candidate keys are all minimal attribute sets that could uniquely identify a row is the best description. The primary key isn’t automatically every candidate key—only one is designated as the primary key. The other options fall short because a candidate key must identify rows (not be unusable), and it doesn’t have to include all attributes (it’s a minimal set, not the entire row).