What is the difference between primary and super key?

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Database keys
What exactly is the difference between primary and super key if both are considered to be unique? Why do we need super key when there is primary key?
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Difference
between primary and super key

Primary Key: is
the columns you choose to maintain uniqueness in a table. Here in Employee
table you can choose    either EmployeeID or SSN columns, EmployeeID is
preferable choice, as SSN is a secure value.

Super Key: If
you add any other column/attribute to a Primary Key then it become a super key,
like EmployeeID + FullName
 is a Super Key.

Check this useful article to know more details    

https://www.mindstick.com/blog/371/sql-keys

https://sqlwithmanoj.com/2014/09/15/db-basics-what-are-candidate-primary-composite-super-keys-and-difference-between-them/

Discuss This Question: 5  Replies

 
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  • Subhendu Sen
    Assuming this is based on home work related to networking course, so if you read the study books, you can find answers easily.
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  • carlosdl
    Subhendu: The topic is not related to networking, but to database design.
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  • carlosdl
    I was asked a similar question a couple of weeks ago, but about candidate keys vs super keys.  It is relevant because a primary key is basically a candidate key.


    This is the answer I gave:

    --------------------

    The main difference between superkey and candidate key is that a super key can have many attributes or columns, even if not all of them are necessary to identify a row.

    For example, in an accounts table, for a bank: You could have a superkey that includes the account number and the name of the customer.

    That combination of fields identifies a row uniquely, but the name is not really necessary.

    Even if you don't include the name, only with the account number you can identify uniquely the same row.

    So, a candidate key is a key that includes only the necessary columns to uniquely identify a row.

    A candidate key doesn't include unnecessary columns.

    In this example account number is a candidate key, but the combination of account number and name would be a super key.

    -----------------
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  • carlosdl
    And to answer the final question: You don't really need super keys. You just need to know what they are (because database courses cover them).
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  • Aishwarya17

    It was of great help.

    Thanks!

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