☞ Keys allow us to identify an attribute or a set of attributes on the on the basis of which a table is identified.
☞ They are used to establish and identify relation among two or more tables.
☞ The different types of keys in a RDBMS are as follows :
1. Primary Key 2. Candidate Key 3. Alternate Key 4. Foreign Key
☞ It is a set of one or more attributes/fields which uniquely identifies a tuple/row in a table.
☞ It is unique in nature.
☞ It arranges the table in its own order.
☞ It cannot be left null.
☞ One table can have only one primary key
☞ It refers to all the attributes in a relation that are candidates or are capable of becoming a primary key.
☞ A candidate key that is not the primary key is called an alternate key.
☞ It is a non-key attribute whose value is derived from the primary key of another table.
