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What is a GUID?

A GUID (Globally Unique Identifier) is a 128-bit number used to uniquely identify resources in computer systems. GUIDs are identical to UUIDs and follow the same RFC-4122 standard.

The term "GUID" is predominantly used in Microsoft technologies:

.NET Framework and .NET Core - using System.Guid
SQL Server - uniqueidentifier data type
COM and Windows API - component identification
Active Directory - object identifiers

GUID Format

A GUID is displayed as 32 hexadecimal digits in 5 groups separated by hyphens:

xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
Example: 550e8400-e29b-41d4-a716-446655440000

GUID in C# / .NET

// Generate a new GUID
Guid newGuid = Guid.NewGuid();

// Parse from string
Guid parsed = Guid.Parse("550e8400-e29b-41d4-a716-446655440000");

// Safe parsing
if (Guid.TryParse(input, out Guid result)) {
    // Use result
}

GUID in SQL Server

-- Generate a new GUID
SELECT NEWID();

-- Create table with GUID primary key
CREATE TABLE Users (
    Id UNIQUEIDENTIFIER DEFAULT NEWID() PRIMARY KEY,
    Name NVARCHAR(100)
);

-- For better index performance, use NEWSEQUENTIALID()
CREATE TABLE Orders (
    Id UNIQUEIDENTIFIER DEFAULT NEWSEQUENTIALID() PRIMARY KEY,
    OrderDate DATETIME
);

Frequently Asked Questions

What is a GUID?

GUID (Globally Unique Identifier) is a 128-bit identifier used primarily in Microsoft technologies. GUIDs are identical to UUIDs (Universally Unique Identifiers) and follow the same RFC-4122 standard. The term GUID is commonly used in .NET, SQL Server, and Windows development.

What is the difference between GUID and UUID?

GUID and UUID are the same thing - both are 128-bit identifiers following RFC-4122. The term GUID is used in Microsoft ecosystems (.NET, SQL Server, COM), while UUID is the standard term used in other contexts like databases, APIs, and cross-platform development.

How do I use a GUID in C# or .NET?

In C#, use Guid.NewGuid() to generate a new GUID. Example: Guid myGuid = Guid.NewGuid(); You can also parse a GUID string using Guid.Parse() or Guid.TryParse() for safe parsing.

How do I create a GUID in SQL Server?

In SQL Server, use the NEWID() function to generate a GUID. For sequential GUIDs (better for indexing), use NEWSEQUENTIALID() as a column default.