What’s the difference between a primary key and a unique key?

 Posted by Lakhangarg on 8/24/2009 | Category: Sql Server Interview questions | Views: 4043

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.

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Posted by: Kapil.j.dhokai on: 9/21/2009
Another Difference are:

--> Table can have only one Primary key, while more than 1 Unique keys.

--> All Table records physically store by primary Kay.

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