Secondary keys in RDBMS

What is a secondary key

A secondary key is a key that has not been selected as a primary key. However, it is considered a candidate key for the primary key.

Therefore, candidate keys that are not selected as primary keys are called secondary keys. A candidate key is an attribute or set of attributes that you can think of as a primary key.

Note: Secondary keys are not foreign keys.

Example

Let’s look at an example −

##096055##9122699Shreyas28 Above, Student_ID, Student_Enroll and

Student_ID	Student_Enroll	Student_Name	##Student_Age	Student_Email
9122717	Manish	25	##aaa@gmail.com
9122655	Manan	23	abc@gmail.com	##067
		##pqr@gmail.com

Student_Email

are candidate keys. They are considered candidate keys because they uniquely identify student records. Select one of the candidate keys as the primary key. The remaining two keys will become secondary keys.

Assume that you selected Student_ID as the primary key, so Student_Enroll and

Student_Email

will become secondary keys (candidate keys for the primary key). ExampleLet’s look at another example −

Employee_ID

E7897 Tomtom@example.comOperationsEmployee_Email are candidate keys. They uniquely identify employee records. Select one of the candidate keys as the primary key. The remaining two keys will become secondary keys.

Employee_No	Employee_Name	Employee_Email	Employee_Dept	##0989
Jacob	##jacob@example.com	Finance	0777	E8768
Anna	anna@example.com	HR	##0656	E8789
				Above, Employee_ID, Employee_No and

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