Key

A key is a field that you use to sort data.

Following are the different types of keys.

1.     Candidate key.

A candidate key is a super key that contains no extra attribute.

2.     Primary Key.

A primary key is a candidate key that is selected by the database designer to identify tuples uniquely in a relation.

3.     Alternate Key.

The candidate keys that are not selected as primary key are known as alternate keys.

4.     Foreign key

A foreign key is an attribute or set of attributes in a relation whose values match a primary key in another relation.

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