1) Partial Keys: A set of attributes that uniquely identifies weak entities, which are related to the same owner entity.
2) Alternate Keys: All candidate keys except the primary key are known as alternate keys.
3) Compound Key: It has multiple fields that enable the user to uniquely recognize a specific record.
4) Artificial Key: It is the extra attribute added to the table when there are no stands alone or compounds key is available. It is created by assigning a number to each record in the table.