Guid in SQL Server: A Comprehensive Guide for Dev

Welcome, Dev, to this comprehensive guide on Guid in SQL Server. Guid, short for Globally Unique Identifier, is a data type used in SQL Server to uniquely identify rows in a table. In this article, we will cover everything you need to know about Guid in SQL Server, from what it is and how it works to best practices and FAQs.

What is Guid?

Guid, also known as UUID (Universally Unique Identifier) or IUID (Intellectual Unique Identifier), is a 16-byte binary number that is generated by an algorithm. It is designed to be unique across all devices and systems in the world, hence the name “globally unique”. Guid is commonly used as a primary key in SQL Server tables to ensure that each row in the table is uniquely identified.

Guid is represented as a string of 32 hexadecimal digits, grouped into 5 sections separated by hyphens. For example, a typical Guid looks like this:

Section	Length	Example
1	8	6F9619FF-8B86-D011-B42D-00C04FC964FF
2	4	8B86
3	4	D011
4	4	B42D
5	12	00C04FC964FF

How is Guid generated?

Guid is generated using a combination of the current date and time, a unique number, and the MAC address of the computer. The algorithm used to generate Guid ensures that each Guid is unique and that there is a very low chance of two Guids being the same.

Why use Guid in SQL Server?

Guid is commonly used as a primary key in SQL Server tables because it provides a high level of uniqueness and avoids the need to generate a unique identifier manually. This can be especially useful in scenarios where data is being replicated across multiple servers, as it ensures that each row in the table is uniquely identified.

When should you not use Guid in SQL Server?

Guids can have a negative impact on performance, especially when they are used as clustered indexes. This is because Guids are not sequential, which can cause page splits and fragmentation in the index. In general, it is recommended to use an integer or bigint data type for primary keys if performance is a concern.

How to declare Guid in SQL Server?

To declare a Guid column in a SQL Server table, you can use the uniqueidentifier data type. For example:

CREATE TABLE MyTable (Id uniqueidentifier PRIMARY KEY,Name nvarchar(50));

Working with Guid in SQL Server

How to insert Guid into SQL Server?

To insert a Guid value into a SQL Server table, you can use the NEWID() function to generate a new Guid. For example:

INSERT INTO MyTable (Id, Name) VALUES (NEWID(), 'John');

You can also assign a Guid value to a variable or column using the CAST function. For example:

DECLARE @myGuid uniqueidentifier;SET @myGuid = CAST('6F9619FF-8B86-D011-B42D-00C04FC964FF' AS uniqueidentifier);INSERT INTO MyTable (Id, Name) VALUES (@myGuid, 'Mary');

How to retrieve Guid from SQL Server?

To retrieve a Guid value from a SQL Server table, you can use the SELECT statement. For example:

SELECT Id, Name FROM MyTable WHERE Id = '6F9619FF-8B86-D011-B42D-00C04FC964FF';

You can also use the CAST function to convert a Guid column to a string. For example:

SELECT CAST(Id AS nvarchar(36)), Name FROM MyTable;

How to update Guid in SQL Server?

To update a Guid value in a SQL Server table, you can use the UPDATE statement. For example:

UPDATE MyTable SET Name = 'Jack' WHERE Id = '6F9619FF-8B86-D011-B42D-00C04FC964FF';

You can also generate a new Guid value using the NEWID() function and update the column with the new value. For example:

UPDATE MyTable SET Id = NEWID() WHERE Name = 'Mary';

How to delete Guid from SQL Server?

To delete a row with a specific Guid value from a SQL Server table, you can use the DELETE statement. For example:

DELETE FROM MyTable WHERE Id = '6F9619FF-8B86-D011-B42D-00C04FC964FF';

Best Practices for Using Guid in SQL Server

Use Sequential Guid for Better Performance

As mentioned earlier, Guids can have a negative impact on performance when they are used as clustered indexes. To mitigate this issue, you can use Sequential Guids instead of Random Guids. Sequential Guids are generated in a sequential manner, which makes them more efficient for indexing. To generate Sequential Guids in SQL Server, you can use the NEWSEQUENTIALID() function instead of the NEWID() function.

Avoid Using Guid as Foreign Keys

Guids can be used as foreign keys in SQL Server, but it is generally not recommended. This is because Guids take up more space than integers and can slow down queries that join tables on foreign keys. It is usually better to use an integer data type for foreign keys.

Don’t Generate Guids in the Application Layer

While it is possible to generate Guids in the application layer, it is generally not recommended. This is because there is a higher chance of generating duplicate Guids if the same algorithm is used across multiple applications or devices. It is better to generate Guids directly in SQL Server using the NEWID() or NEWSEQUENTIALID() functions.

Consider Hybrid Approaches

In some cases, it may be beneficial to use a hybrid approach where Guids are used for primary keys and integers are used for foreign keys. This approach can provide the benefits of Guids while minimizing their drawbacks.

FAQ

What is the difference between Guid and UUID?

Guid and UUID are interchangeable terms that refer to the same data type. Guid is the term used by Microsoft and UUID is the term used by the rest of the industry.

Can Guids be used as primary keys in all scenarios?

Guids can be used as primary keys in most scenarios, but there are some cases where it may not be appropriate. For example, if you have a large table with millions of rows, using Guids as primary keys can have a negative impact on performance.

What is the maximum length of a Guid in SQL Server?

The maximum length of a Guid in SQL Server is 36 characters, including the hyphens.

Can Guids be used across multiple SQL Server instances?

Yes, Guids can be used across multiple SQL Server instances as long as they are generated using the same algorithm. This ensures that each Guid is unique across all instances.

Can Guids be generated using a custom algorithm?

Yes, it is possible to generate Guids using a custom algorithm. However, it is generally not recommended as it can lead to compatibility issues across different systems.

That’s it for our comprehensive guide on Guid in SQL Server, Dev. We hope you found this article helpful and informative. If you have any further questions or comments, please feel free to leave them below.