Purushottam Rathore
What's the difference between a primary key and a unique key?
By Purushottam Rathore in SQL Server on Jul 29 2009
  • Ramprit Sahani
    Jan, 2015 30

    Primary Doesn't allow any dublicate value and null value. But unique allow only one null value. simple and easy

    • 0
  • Pradeep
    Aug, 2009 18

    Hi,

    You can have multiple unique keys in a table but can have only one Primary Key.
    Primary key and unique key does not allow enter duplicate data.Primary key doesn't allow null value.Unique key allows only one null value.


    • 0
  • Purushottam Rathore
    Jul, 2009 29

    Both primary key and unique enforce uniqueness of the column on which
    they are defined. But by default primary key creates a clustered index
    on the column, where are unique creates a nonclustered index by
    default. Another major difference is that, primary key doesn't allow
    NULLs, but unique key allows one NULL only.

    • 0


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