How to Get a New GUID in SQL: A Comprehensive Guide

In SQL Server, a Globally Unique Identifier (GUID), also known as a UUID (Universally Unique Identifier), is a 128-bit integer number used to identify information in computer systems. GUIDs are practically unique, meaning the chance of the same GUID being generated twice is astronomically low. This makes them ideal for use as primary keys in databases, especially in distributed systems, or anywhere else where you need a unique identifier that doesn’t require coordination across multiple systems. This article delves into how to get a new GUID in SQL, including syntax, examples, and best practices.

Understanding NEWID() Function

The primary way to generate a new GUID in SQL Server is by using the NEWID() function. This function returns a unique value of the uniqueidentifier data type. NEWID() is compliant with RFC4122, ensuring a high degree of uniqueness and compatibility.

Syntax of NEWID()

The syntax for using the NEWID() function is straightforward:

NEWID()

It takes no arguments and returns a uniqueidentifier.

Return Type

The NEWID() function returns a value of type uniqueidentifier.

Practical Examples of Using NEWID()

Here are several examples demonstrating how to use the NEWID() function in various scenarios.

A. Assigning a GUID to a Variable

This example demonstrates how to declare a variable of type uniqueidentifier and assign it a new GUID using NEWID().

-- Declaring a local variable
DECLARE @myid uniqueidentifier;
SET @myid = NEWID();
PRINT 'Value of @myid is: ' + CONVERT(varchar(255), @myid);

This code snippet first declares a variable named @myid with the uniqueidentifier data type. Then, it uses the SET statement to assign a new GUID generated by NEWID() to the variable. Finally, it prints the value of the variable. Note that the GUID generated will be different each time the code is run.

B. Using NEWID() in a CREATE TABLE Statement

This example shows how to create a table with a uniqueidentifier column and use NEWID() as a default value for that column. This ensures that every new row inserted into the table will automatically have a unique GUID assigned.

-- Creating a table using NEWID for uniqueidentifier data type
CREATE TABLE cust (
    CustomerID uniqueidentifier NOT NULL DEFAULT NEWID(),
    Company VARCHAR(30) NOT NULL,
    ContactName VARCHAR(60) NOT NULL,
    Address VARCHAR(30) NOT NULL,
    City VARCHAR(30) NOT NULL,
    StateProvince VARCHAR(10) NULL,
    PostalCode VARCHAR(10) NOT NULL,
    CountryRegion VARCHAR(20) NOT NULL,
    Telephone VARCHAR(15) NOT NULL,
    Fax VARCHAR(15) NULL
);
GO

-- Inserting 5 rows into cust table
INSERT cust (Company, ContactName, Address, City, StateProvince, PostalCode, CountryRegion, Telephone, Fax)
VALUES
    ('Wartian Herkku', 'Pirkko Koskitalo', 'Torikatu 38', 'Oulu', NULL, '90110', 'Finland', '981-443655', '981-443655'),
    ('Wellington Importadora', 'Paula Parente', 'Rua do Mercado, 12', 'Resende', 'SP', '08737-363', 'Brasil', '(14) 555-8122', ''),
    ('Cactus Comidas para Ilevar', 'Patricio Simpson', 'Cerrito 333', 'Buenos Aires', NULL, '1010', 'Argentina', '(1) 135-5555', '(1) 135-4892'),
    ('Ernst Handel', 'Roland Mendel', 'Kirchgasse 6', 'Graz', NULL, '8010', 'Austria', '7675-3425', '7675-3426'),
    ('Maison Dewey', 'Catherine Dewey', 'Rue Joseph-Bens 532', 'Bruxelles', NULL, 'B-1180', 'Belgium', '(02) 201 24 67', '(02) 201 24 68');
GO

In this example, the CustomerID column is defined as uniqueidentifier NOT NULL DEFAULT NEWID(). This means that if you insert a new row into the cust table without specifying a value for the CustomerID column, SQL Server will automatically generate a new GUID and assign it to that column.

C. Explicitly Assigning a GUID

This example shows how to declare a uniqueidentifier variable and explicitly assign a specific GUID value to it. Note that this approach doesn’t generate a new GUID, but rather uses a pre-existing one.

DECLARE @myid uniqueidentifier;
SET @myid = 'A972C577-DFB0-064E-1189-0154C99310DAAC12';
SELECT @myid;
GO

This is useful when you need to work with a specific GUID, rather than generating a new one.

D. Querying Random Data with NEWID()

The NEWID() function can also be used to retrieve random data from a table. This is achieved by using NEWID() in the ORDER BY clause.

SELECT TOP 1 ProductID, Name, ProductNumber
FROM Production.Product
ORDER BY NEWID();
GO

This query selects the ProductID, Name, and ProductNumber from the Production.Product table. The ORDER BY NEWID() clause sorts the rows randomly, and TOP 1 selects only the first row, effectively returning a random record. Increasing the TOP value will return more random records.

E. Using NEWID() in Azure Synapse Analytics

NEWID() is also supported in Azure Synapse Analytics, allowing you to generate unique identifiers in your data warehouse environment. The syntax and usage are the same as in SQL Server.

Best Practices and Considerations

• Uniqueness: While NEWID() generates practically unique identifiers, it’s not guaranteed to be 100% unique. If absolute uniqueness is critical, consider implementing additional checks or using other methods for generating unique identifiers.
• Performance: Using NEWID() in the ORDER BY clause for large tables can impact performance due to the need to generate a new GUID for each row. Consider the performance implications when using NEWID() in queries that process large datasets.
• Storage: The uniqueidentifier data type requires 16 bytes of storage. Keep this in mind when designing your database schema, especially for tables with a large number of rows.

Alternatives to NEWID()

While NEWID() is the standard way to generate GUIDs in SQL Server, there are alternative approaches:

• Application-level GUID generation: You can generate GUIDs in your application code (e.g., using .NET’s Guid.NewGuid() method) and pass them to SQL Server as parameters. This can be useful if you need to generate GUIDs before inserting data into the database.
• Sequences: For some scenarios, sequences might be a suitable alternative to GUIDs. Sequences generate sequential numbers, which can be more efficient for indexing and querying in certain cases. However, sequences don’t provide the same level of uniqueness as GUIDs, especially in distributed systems.

Conclusion

The NEWID() function is a powerful tool for generating unique identifiers in SQL Server. Understanding how to use NEWID() effectively is essential for designing robust and scalable database applications. By following the examples and best practices outlined in this article, you can confidently implement GUIDs in your SQL Server databases.