Key Type |
Definition |
Superkey |
An attribute (or combination of attributes) that uniquely identifies each row in a table |
Candidate key |
A minimal superkey. A superkey that does not contain a subset of attributes that is itself a superkey
|
Primary key |
A candidate key selected to uniquely identify all other attribute values in any given row. Cannot contain null entries. |
Secondary key |
An attribute(or combination of attributes) used strictly for data retrieval purposes. |
Foreign key |
An attribute(or combination of attributes) in one table whose value must either match the primary key in another table or be null. |
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