Secondary Key in RDBMS

RDBMSDatabaseMySQL

What is a Secondary Key

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

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

Note: Secondary Key is not a Foreign Key.

Example

Let us see an example −

Student_ID
Student_Enroll
Student_Name
Student_Age
Student_Email
096
9122717
Manish
25
aaa@gmail.com
055
9122655
Manan
23
abc@gmail.com
067
9122699
Shreyas
28
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 key. Rest of the two keys would be Secondary Key.

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

Example

Let us see another example −

Employee_ID
Employee_No
Employee_Name
Employee_Email
Employee_Dept
0989
E7897
Jacob
jacob@example.com
Finance
0777
E8768
Anna
anna@example.com
HR
0656
E8789
Tom
tom@example.com
Operations


Above, Employee_ID, Employee_No and Employee_Email are the candidate keys. They uniquely identify the Employee record. Select any one of the candidate key as the primary key. Rest of the two keys would be Secondary Key.

raja
Published on 04-Jul-2018 00:06:31
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