What Is Uniqueidentifier Data Type in SQL Server?


Angela Bailey

What Is Uniqueidentifier Data Type in SQL Server?

In SQL Server, the uniqueidentifier data type is used to store globally unique identifiers (GUIDs). A GUID is a 128-bit integer value that is generated using an algorithm designed to ensure its uniqueness across all computers and networks.

Why Use Uniqueidentifier?

The uniqueidentifier data type can be particularly useful in scenarios where you need to:

  • Create surrogate primary keys that are globally unique.
  • Generate identifiers for distributed databases or systems.
  • Combine data from multiple sources without conflicts.


The syntax to declare a column with the uniqueidentifier data type in SQL Server is as follows:

    ColumnName uniqueidentifier

You can also assign a default value to a uniqueidentifier column:

    ColumnName uniqueidentifier DEFAULT NEWID()

Generating Uniqueidentifiers:

The most common way to generate uniqueidentifiers in SQL Server is by using the NEWID() function. This function returns a new globally unique identifier each time it is called. Here’s an example of how to use it:

INSERT INTO TableName (ColumnName)

You can also use the NEWSEQUENTIALID() function, which generates sequential but still unique identifiers. However, it should be noted that this function may not guarantee strict uniqueness in certain scenarios due to its implementation details.

Working with Uniqueidentifiers:

When working with uniqueidentifiers, it’s important to keep in mind the following:

  • Uniqueidentifiers have a fixed size of 16 bytes.
  • They are represented as a string of 32 hexadecimal digits separated by hyphens.
  • Uniqueidentifiers can be compared and sorted using the ORDER BY clause.
  • The UNIQUEIDENTIFIER data type is case-insensitive, meaning that ‘ABC’ and ‘abc’ are considered the same value.


The uniqueidentifier data type in SQL Server allows you to store globally unique identifiers. It is particularly useful when you need to create surrogate primary keys or generate identifiers for distributed systems. By using the appropriate functions, such as NEWID(), you can easily generate uniqueidentifiers and work with them effectively in your SQL queries.

Incorporating the uniqueidentifier data type into your database design can enhance data integrity and provide a reliable way to identify records across multiple systems or databases.

Note: Uniqueidentifiers should be used judiciously, as they may consume more storage space compared to other data types and could impact performance if used excessively.

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