How NEWID() is Generated

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SQL-Server-2005

Dear Friends,

I have used NewID() in SQL which give me the Unique ID.
But I want to know on what bases it is generated.

Eg: SELECT NEWID()

Posted 15-Aug-12 0:31am

Arunprasath Natarajan

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Solution 1

NewID generates a Globally Unique IDentifier, or GUID. This is a 128 bit number which means that there is less chance of getting a duplicate value that there is of you winning the lottery.

This week.

And next week.

And every single week from now to the end of your life.

The generated value is not truly unique, but the odds are so high that they can be treated as unique values for all practical purposes.

Posted 15-Aug-12 0:52am

OriginalGriff

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Arunprasath Natarajan 15-Aug-12 7:51am

Tan q, Can you give me the logic of its generation...

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StianSandberg · Accepted Answer · 2012-08-15T02:09:00

A Guid is 32 hex digits grouped into chunks of 8-4-4-4-12. Number of unique Guids is 2^128. Thats a lot..
Guids are created in different ways. The most used Guid is a version 4 Guid based on Time, MAC-address and Random data. (the first number of 3rd chunk is the version number)

            version
              |     
542DF77C-B284-4623-9BC8-FD1E9343CD2C
1A32EAFB-28DD-4E4A-AD27-58B9DD301CD9
87FD5B4E-E733-4B18-951E-F6EBC8960D22
DCE7501C-D419-424A-8C5B-FBE2589AFB73
B056348F-3E4A-4739-87A9-7872FB083295

Since it's using both Mac-address and Time, the only way to create a duplicate Guid is to adjust them clock on your server back in time and try to regenerate a duplicate. You'll never manage to create duplicates, but i theory you can.