3. Explain the difference between a primary key, a composite key, a
super key, a candidate key, and a secondary key.
|
Primary Key |
An attribute which
uniquely identifies a record (entity instance) |
|
Composite Key |
A combination of keys
(concatenated key) which can be used to uniquely identify a record (entity
instance) |
|
Super Key |
Either a Primary key or
Composite Key |
|
Candidate Key |
A key, or group of keys
(composite keys) which may become a primary key |
|
Secondary Key |
Any key, or group of keys,
which can NOT be considered for entry as a superkey |