Which type of database key is a candidate key that has not been chosen as the primary key?

An Alternate Key is any candidate key that is not selected as the primary key of the table. Candidate keys are attributes (or combinations of attributes) that uniquely identify a row in a table. Among these, one is chosen as the primary key, while others are considered alternate keys. For example, in a table of students, both StudentID and Email might uniquely identify records. If StudentID is the primary key, Email becomes an alternate key. Alternate keys are useful for additional indexing or as foreign keys in related tables. Why Other Options Are Incorrect :

1. Foreign Key : A foreign key establishes a relationship between two tables, linking a column to the primary key in another table.
2. Composite Key : A composite key is made of two or more columns together acting as a primary key.
3. Surrogate Key : This is a system-generated unique identifier for a row, not derived from application data.
4. Super Key : A super key is a broader set of attributes that can uniquely identify a row, which may contain unnecessary attributes.