Answer
A superkey is any set of attributes that uniquely identifies a row. • It may contain unnecessary extra attributes. • A candidate key is a minimal superkey. • Database constraints should enforce the real keys used by the design.
💡 SQL Example
SELECT user_id, email FROM users;
Result
user_id alone and user_id plus email can both be superkeys
⚡ Quick Revision
A superkey uniquely identifies rows; a candidate key is minimal.