Keys are very important part of Relational database. They are used to
establish and identify relation between tables. They also ensure that
each record within a table can be uniquely identified by combination of
one or more fields within a table.
Super Key
Super Key is defined as a set of attributes within a table that
uniquely identifies each record within a table. Super Key is a super set
of Candidate key.
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.
Primary Key
Primary key is a candidate key that is most appropriate to become
main key of the table. It is a key that uniquely identify each record in
a table.
Composite Key
Key that consist of two or more attributes that uniquely identify an entity occurrence is called
Composite key. But any attribute that makes up the
Composite key is not a simple key in its own.
Secondary or Alternative key
The candidate key which are not selected for primary key are known as secondary keys or alternative keys
Non-key Attribute
Non-key attributes are attributes other than
candidate key attributes in a table.
Non-prime Attribute
Non-prime Attributes are attributes other than
Primary attribute.
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