Types of keys with example in DBMS(Data Base Management System)

•  Key is used to uniquely identify any record present in the table.
• A DBMS Key can be an attribute or a set of attributes which helps to identify a record of a table.

For Example :

• Types of key:

1. Primary key
2. Candidate key
3. Super Key
4. Foreign key
5. Alternate key

1) Primary key :

• Primary key is used to identify one instance of an entity uniquely.
• Table can have multiple keys, the key which is most suitable from those lists become a primary key.
• Selection of primary key in table is completly based on requirement and developers.

For example :

2) Candidate key :

• It is an attribute or set of an attribute that can uniquely identify a tuple.
• The candidate key can having only one attribute or composite as well.

For example :

Here PRN and Adhar card column is a candidate key

3) Super Key :

• It is a set of an attribute that can uniquely identify a tuple.
• In Super key there is no restriction on number of attributes, it may consist of any number of attributes

For example :

4) Foreign key :

• To point to the primary key of another table foreign key columns are used.
• Foreign Key is used to establish relationships between two tables

5)  Alternate key :

Those candidate keys which are not the Primary key are Alternate

keys.