Alternate Key in RDBMS

RDBMSDatabaseMySQL

Alternate Key or Secondary Key is the key that has not been selected to be the primary key, but are candidate keys. However, it is considered a candidate key for the primary key.

A candidate key not selected as a primary key is called alternate or secondary key. Candidate key is an attribute or set of attributes that you can consider as a Primary key.

Let us see an example −

Student_ID
Student_Enroll
Student_Name
Student_Email
096
2717
Manish
aaa@gmail.com
055
2655
Manan
abc@gmail.com
067
2699
Shreyas
pqr@gmail.com

Above, Student_ID, Student_Enroll and Student_Email are the candidate keys. They are considered candidate keys since they can uniquely identify the student record. Select any one of the candidate key as the primary. Rest of the two keys would be Alternate or Secondary Key.

Let’s say you selected Student_ID as primary key, therefore Student_Enroll and Student_Email will be Alternate Key (candidates of primary key).

Let us see another example −

<Employee>

Employee_ID
Employee_SSN
Employee_Name
Employee_Phone
E897
SSN08
Harry
999999
E856
SSN06
Jacob
999899
E871
SSN09
Amy
999898

In the above table, the following are the three candidate keys −

Employee_ID
Employee_SSN
Employee_Phone

Select any one of the above key as Primary Key, for example, EmployeeSSN. The rest of the two keys would then be called Alternate Keys because they were candidates of Primary Key.

Therefore, Employee_SSN and Employee_Phone are Alternate Keys.

raja
Published on 04-Jul-2018 13:52:52
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