Is Uniqueidentifier a Data Type?


Scott Campbell

Is Uniqueidentifier a Data Type?

In SQL Server, the uniqueidentifier is indeed a data type. It is used to store a globally unique identifier (GUID) value in a database table. A GUID is a 128-bit number that is generated by an algorithm and is guaranteed to be unique across all computers and networks.

What is a GUID?

A GUID, as mentioned earlier, stands for globally unique identifier. It serves as a primary key in many databases where uniqueness is of utmost importance. You can think of it as a fingerprint that identifies a particular record in a database table.

In most cases, GUIDs are generated using algorithms that take into account various factors like the current time, network MAC address, and random numbers. This ensures that the probability of two or more GUIDs having the same value is extremely low.

How to Declare and Use Uniqueidentifier

To declare a column with the uniqueidentifier data type in SQL Server, you can use the following syntax:

    ID uniqueidentifier PRIMARY KEY,
    Name varchar(50)

The uniqueidentifier data type can also be used as part of composite primary keys or foreign keys in relationships between tables.

Generating Uniqueidentifiers

You can generate uniqueidentifiers using various methods:

  • NewID(): This function generates a new uniqueidentifier value based on the current machine’s network card address and current timestamp.
  • NewSequentialID(): This function generates sequential uniqueidentifier values based on an internal algorithm. It may perform better than NewID() in certain scenarios.
  • Application Code: You can also generate uniqueidentifiers in your application code using libraries or built-in functions specific to the programming language you are using.

Once generated, uniqueidentifiers can be stored in the database and used for various purposes like record identification, referencing related data, or generating audit trails.


The uniqueidentifier data type is an essential part of SQL Server’s data modeling capabilities. It allows for the storage and manipulation of globally unique identifiers, ensuring data integrity and uniqueness across multiple systems. By understanding how to declare and generate uniqueidentifiers, you can use this data type effectively in your database design.

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