Answer
A candidate key is a minimal set of attributes that can uniquely identify a row. • Minimal means no proper subset is also unique. • One candidate key is chosen as the primary key. • Other candidate keys can be enforced with UNIQUE and NOT NULL constraints.
💡 SQL Example
CREATE TABLE users (user_id integer PRIMARY KEY, email text UNIQUE NOT NULL);
Result
CREATE TABLE
⚡ Quick Revision
Candidate keys are minimal unique row identifiers.