CANDIDATE KEY: - Candidate keys are defined as the set of fields from which primary key can be
selected. It is an attribute or set of attribute that can act as a primary key for a table to uniquely identify each
record in that table.
COMPOSITE KEY:- Key that consists of two or more attributes that uniquely identify an entity is
called Composite key. But any attribute that makes up the Composite key is not a simple key in its own.