Transact-SQL Reference


SQL Server 2008 Books Online (October 2009)
NEWSEQUENTIALID() (Transact-SQL)

Updated: 30 September 2009

Creates a GUID that is greater than any GUID previously generated by this function on a specified computer since Windows was started. After restarting Windows, the GUID can start again from a lower range, but is still globally unique. When a GUID column is used as a row identifier, using NEWSEQUENTIALID can be faster than using the NEWID function. This is because the NEWID function causes random activity and uses fewer cached data pages. Using NEWSEQUENTIALID also helps to completely fill the data and index pages.

ms189786.note(en-us,SQL.100).gifImportant:
If privacy is a concern, do not use this function. It is possible to guess the value of the next generated GUID and, therefore, access data associated with that GUID.

NEWSEQUENTIALID is a wrapper over the Windows UuidCreateSequential function.

Topic link icon Transact-SQL Syntax Conventions

Syntax
NEWSEQUENTIALID ( )
Return Type

uniqueidentifier

Remarks

NEWSEQUENTIALID() can only be used with DEFAULT constraints on table columns of type uniqueidentifier. For example: 

CREATE TABLE myTable (ColumnA uniqueidentifier DEFAULT NEWSEQUENTIALID())

When NEWSEQUENTIALID() is used in DEFAULT expressions, it cannot be combined with other scalar operators. For example, you cannot execute the following:

CREATE TABLE myTable (ColumnA uniqueidentifier DEFAULT dbo.myfunction(NEWSEQUENTIALID()))

In the previous example, myfunction() is a scalar user-defined scalar function that accepts and returns a uniqueidentifier value.

NEWSEQUENTIALID() cannot be referenced in queries.

You can use NEWSEQUENTIALID() to generate GUIDs to reduce page contention at the leaf level of indexes.

Each GUID generated by using NEWSEQUENTIALID() is unique on that computer. GUIDs generated by using NEWSEQUENTIALID() are unique across multiple computers only if the source computer has a network card. For more information about GUIDs, see Using uniqueidentifier Data.

Change History

Updated content

Added a description about the effect that restarting Windows can have on GUIDs.
See Also

Reference

NEWID (Transact-SQL)
Comparison Operators (Transact-SQL)

Help and Information

Getting SQL Server 2008 Assistance
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Community Content

Phil Brammer
Not always sequential (or not always larger than the previous value)
Restarting the OS can setup a situation where a new GUID value generated by NEWSEQUENTIALID() is less than the previous maximum value it generated. See https://connect.microsoft.com/SQLServer/feedback/ViewFeedback.aspx?FeedbackID=475131 for an example.

So just be aware - it is not necessarily sequential.
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Thomas Lee
SQL Server unique identifier solution

Refer to my blog for best practice for SQL Server uniqueidentifier and replication.

Jeff Fischer


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