checksum-agg-transact-sql.md

title	CHECKSUM_AGG (Transact-SQL) | Microsoft Docs
ms.custom
ms.date	07/24/2017
ms.prod	sql
ms.prod_service	database-engine, sql-database
ms.reviewer
ms.technology	t-sql
ms.topic	language-reference
f1_keywords	CHECKSUM_AGG CHECKSUM_AGG_TSQL
dev_langs	TSQL
helpviewer_keywords	checksum values CHECKSUM_AGG function groups [SQL Server], checksum values
ms.assetid	cdede70c-4eb5-4c92-98ab-b07787ab7222
author	MikeRayMSFT
ms.author	mikeray

CHECKSUM_AGG (Transact-SQL)

[!INCLUDEtsql-appliesto-ss2008-asdb-xxxx-xxx-md]

This function returns the checksum of the values in a group. CHECKSUM_AGG ignores null values. The OVER clause can follow CHECKSUM_AGG.

Transact-SQL Syntax Conventions

Syntax

CHECKSUM_AGG ( [ ALL | DISTINCT ] expression )  

Arguments

ALL
Applies the aggregate function to all values. ALL is the default argument.

DISTINCT
Specifies that CHECKSUM_AGG returns the checksum of unique values.

expression
An integer expression. CHECKSUM_AGG does not allow use of aggregate functions or subqueries.

Return types

Returns the checksum of all expression values as int.

Remarks

CHECKSUM_AGG can detect changes in a table.

The CHECKSUM_AGG result does not depend on the order of the rows in the table. Also, CHECKSUM_AGG functions allow the use of the DISTINCT keyword and the GROUP BY clause.

If an expression list value changes, the list checksum value list will also probably change. However, a small possibility exists that the calculated checksum will not change.

CHECKSUM_AGG has functionality similar to that of other aggregate functions. For more information, see Aggregate Functions (Transact-SQL).

Examples

These examples use CHECKSUM_AGG to detect changes in the Quantity column of the ProductInventory table in the [!INCLUDEssSampleDBnormal] database.

--Get the checksum value before the column value is changed.  

SELECT CHECKSUM_AGG(CAST(Quantity AS int))  
FROM Production.ProductInventory;  
GO  

[!INCLUDEssResult]

------------------------  
262  

UPDATE Production.ProductInventory   
SET Quantity=125  
WHERE Quantity=100;  
GO  

--Get the checksum of the modified column.  
SELECT CHECKSUM_AGG(CAST(Quantity AS int))  
FROM Production.ProductInventory;  

[!INCLUDEssResult]

------------------------  
287  

See also

CHECKSUM (Transact-SQL)
HASHBYTES (Transact-SQL)
BINARY_CHECKSUM (Transact-SQL) OVER Clause (Transact-SQL)