Alternate key in DBMS

As we have seen in the candidate key guide that a table can have multiple candidate keys. Among these candidate keys, only one key gets selected as primary key, the remaining keys are known as alternative or secondary keys.

Alternate Key Example

Lets take an example to understand the alternate key concept. Here we have a table Employee, this table has three attributes: Emp_Id, Emp_Number & Emp_Name.

Table: Employee/strong>

Emp_Id  Emp_Number   Emp_Name
------  ----------   --------
E01	2264	     Steve
E22	2278	     Ajeet
E23	2288	     Chaitanya
E45	2290	     Robert

There are two candidate keys in the above table:
{Emp_Id}
{Emp_Number}

DBA (Database administrator) can choose any of the above key as primary key. Lets say Emp_Id is chosen as primary key.

Since we have selected Emp_Id as primary key, the remaining key Emp_Number would be called alternative or secondary key.