Do I need a Identity Specification(self increment) column if I already have a unique column that I can use as key?

Hi, I'm using ms sql 2012.
I'm creating a user table and I wonder when is the case when I should have a self infringement column as a Key for the table?  I'm already going to store Windows users ID in this table so shouldn't I just use this as the key?  Is there any reason that I shouldn't or there is some advantage using the Int Identity Specification type column?
thank you.
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Jim HornMicrosoft SQL Server Data DudeCommented:
Two reasons to use an identity field


An int is only 4 bytes, whereas a character column is going to be roughly one byte per character, depending on unicode or varchar.


If you're ever in a situation where the Windows user id changes due to marriage, divorce, sex change, inserting a new domain's worth of people, whatever, then you're covered. If neither of these are that big a deal, then go ahead and use the Windows user id.

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Kent OlsenDBACommented:
Any unique key can be used as a foreign key.

Note that an integer is typically the fastest data type for join operations.  If your key is a string you should consider changing the key to an IDENTITY column for performance purposes.

Also, the IDENTITY value will never change.  Data can change.  And if you're using data as your primary key you run the risk of conversion/migration issues if you ever need to change the data.

lapuccaAuthor Commented:
Makes a lot of sense.  Thank you.
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