CHECKSUM_AGG
Returns the checksum of the values in a group. Null values are ignored.
Syntax
CHECKSUM_AGG ( [ ALL | DISTINCT ] expression )
Arguments
ALL
Applies the aggregate function to all values. ALL is the default.
DISTINCT
Specifies that CHECKSUM_AGG return the checksum of unique values.
expression
Is a constant, column, or function, and any combination of arithmetic, bitwise, and string operators. expression is an expression of the int data type. Aggregate functions and subqueries are not allowed.
Return Types
Returns the checksum of all expression values as int.
Remarks
CHECKSUM_AGG can be used along with BINARY_CHECKSUM to detect changes in a table.
The order of the rows in the table does not affect the result of CHECKSUM_AGG. In addition, CHECKSUM_AGG functions may be used with the DISTINCT keyword and the GROUP BY clause.
If one of the values in the expression list changes, the checksum of the list also usually changes. However, there is a small chance that the checksum will not change.
CHECKSUM_AGG has similar functionality with other aggregate functions. For more information, see Aggregate Functions.
Examples
A. Use CHECKSUM_AGG with BINARY_CHECKSUM to detect changes in a table.
This example uses CHECKSUM_AGG with the BINARY_CHECKSUM function to detect changes in the Products table.
USE Northwind
GO
SELECT CHECKSUM_AGG(BINARY_CHECKSUM(*))
FROM Products
B. Use CHECKSUM_AGG with BINARY_CHECKSUM to detect changes in a column of a table.
This example detects changes in UnitsInStock column of the Products table in the Northwind database.
--Get the checksum value before the column value is changed.
USE Northwind
GO
SELECT CHECKSUM_AGG(CAST(UnitsInStock AS int))
FROM Products
Here is the result set:
57
--Change the value of a row in the column
UPDATE Products --
SET UnitsInStock=135
WHERE UnitsInStock=125
--Get the checksum of the modified column.
SELECT CHECKSUM_AGG(CAST(UnitsInStock AS int))
FROM Products
Here is the result set:
195