What Data Type Is Uniqueidentifier?


Angela Bailey

What Data Type Is Uniqueidentifier?

A uniqueidentifier is a data type in SQL Server that is used to store a globally unique identifier (GUID). A GUID is a 128-bit integer value that is generated by algorithms and is guaranteed to be unique across all computers and networks.

Why Use Uniqueidentifier?

Uniqueidentifiers are commonly used in situations where it is important to have globally unique identifiers. They are commonly used as primary keys in database tables, ensuring that each row has a unique identifier.

One of the advantages of using uniqueidentifiers is that they can be generated independently of the database. This means that you can generate a uniqueidentifier in your application code and then use it to insert records into the database.

How Are Uniqueidentifiers Generated?

Uniqueidentifiers are typically generated using algorithms that take into account various factors, such as the current timestamp, network card MAC address, and random numbers. This ensures that the generated identifier is highly likely to be globally unique.

The algorithm used to generate uniqueidentifiers guarantees uniqueness even if multiple machines generate them simultaneously.

Storing Uniqueidentifiers

In SQL Server, you can store uniqueidentifiers in a column of type uniqueidentifier. The syntax for creating a table with a column of type uniqueidentifier would look like this:


You can insert values into a column of type uniqueidentifier by providing a valid GUID value:

VALUES ('6F9619FF-8B86-D011-B42D-00C04FC964FF', .)

Working with Uniqueidentifiers

When working with uniqueidentifiers in SQL Server, there are a few things to keep in mind:

  • Comparison: Uniqueidentifiers can be compared using standard comparison operators such as equal to (=) and not equal to (!=).
  • Indexing: Uniqueidentifiers can be used as the primary key of a table and can also be indexed for efficient searching and retrieval.
  • Performance: Uniqueidentifiers are 16 bytes in size, which makes them larger than integer types. This can impact the performance of queries and storage requirements.


The uniqueidentifier data type in SQL Server is a powerful tool for generating and storing globally unique identifiers. It is commonly used as a primary key in database tables and offers several advantages such as independence from the database and guaranteed uniqueness. However, it is important to consider the potential impact on performance when using uniqueidentifiers due to their larger size.

Note: The uniqueidentifier data type is specific to SQL Server. Other databases may have similar data types with different names or functionality.

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