---
title: "Comparing GUID and uniqueidentifier values"
description: "Demonstrates how to work with GUID and uniqueidentifier values in SQL Server and .NET."
ms.date: "09/30/2019"
dev_langs: 
  - "csharp"
ms.assetid: aababd75-2335-43e3-ace8-4b7ae84191a8
ms.prod: sql
ms.prod_service: connectivity
ms.technology: connectivity
ms.topic: conceptual
author: David-Engel
ms.author: v-daenge
ms.reviewer: v-kaywon
---
# Comparing GUID and uniqueidentifier values

[!INCLUDE[Driver_ADONET_Download](../../../includes/driver_adonet_download.md)]

The globally unique identifier (GUID) data type in SQL Server is represented by the `uniqueidentifier` data type, which stores a 16-byte binary value. A GUID is a binary number, and its main use is as an identifier that must be unique in a network that has many computers at many sites. GUIDs can be generated by calling the Transact-SQL NEWID function, and is guaranteed to be unique throughout the world. For more information, see [uniqueidentifier (Transact-SQL)](../../../t-sql/data-types/uniqueidentifier-transact-sql.md).  
  
## Working with SqlGuid values  
Because GUIDs values are long and obscure, they are not meaningful for users. If randomly generated GUIDs are used for key values and you insert a lot of rows, you get random I/O into your indexes, which can negatively impact performance. GUIDs are also relatively large when compared to other data types. In general we recommend using GUIDs only for very narrow scenarios for which no other data type is suitable.  
  
### Comparing GUID values  
Comparison operators can be used with `uniqueidentifier` values. However, ordering is not implemented by comparing the bit patterns of the two values. The only operations that are allowed against a `uniqueidentifier` value are comparisons (=, <>, \<, >, \<=, >=) and checking for NULL (IS NULL and IS NOT NULL). No other arithmetic operators are allowed.  
  
Both <xref:System.Guid> and <xref:System.Data.SqlTypes.SqlGuid> have a `CompareTo` method for comparing different GUID values. However, `System.Guid.CompareTo` and `SqlTypes.SqlGuid.CompareTo` are implemented differently. <xref:System.Data.SqlTypes.SqlGuid> implements `CompareTo` using SQL Server behavior, in the last six bytes of a value are most significant. <xref:System.Guid> evaluates all 16 bytes. The following example demonstrates this behavioral difference. The first section of code displays unsorted <xref:System.Guid> values, and the second section of code shows the sorted <xref:System.Guid> values. The third section shows the sorted <xref:System.Data.SqlTypes.SqlGuid> values. The output is displayed beneath the code listing.  
  
[!code-csharp[DataWorks SqlGuid#1](~/../sqlclient/doc/samples/SqlGuid.cs#1)]
  
This example produces the following results.  
  
```console
Unsorted Guids:  
3aaaaaaa-bbbb-cccc-dddd-2eeeeeeeeeee  
2aaaaaaa-bbbb-cccc-dddd-1eeeeeeeeeee  
1aaaaaaa-bbbb-cccc-dddd-3eeeeeeeeeee  
  
Sorted Guids:  
1aaaaaaa-bbbb-cccc-dddd-3eeeeeeeeeee  
2aaaaaaa-bbbb-cccc-dddd-1eeeeeeeeeee  
3aaaaaaa-bbbb-cccc-dddd-2eeeeeeeeeee  
  
Sorted SqlGuids:  
2aaaaaaa-bbbb-cccc-dddd-1eeeeeeeeeee  
3aaaaaaa-bbbb-cccc-dddd-2eeeeeeeeeee  
1aaaaaaa-bbbb-cccc-dddd-3eeeeeeeeeee  
```  
  
## Next steps
- [SQL Server data types and ADO.NET](sql-server-data-types.md)