CHECKSUM_AGG function is used to get checksum of values in a group. It ignores null values in computation.

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.

Syntax of CHECKSUM function :

CHECKSUM ( * | expression [ ,...n ] )

* means that the computation is over all the columns of the table.

Expression is any valid sql expression of any type.

Example of CHECKSUM function :

Example 1 : Use of CHECKSUM_AGG function in SELECT clause to get checksum in group

SELECT   CHECKSUM_AGG(CONVERT(INT,UnitsInStock))

FROM   Products

Output

 50

Now update some of the rows and again run the query.

UPDATE Products

SET         UnitsInStock = 15

WHERE  UnitsInStock < 10

SELECT  CHECKSUM_AGG(CONVERT(INT,UnitsInStock))

FROM     Products

Output

61

Above example displays checksum of unit price field in the products table.

Example 2 : Using CHECKSUM_AGG function with BINARY_CHECKSUM to detect changes in a table

SELECT  CHECKSUM_AGG(BINARY_CHECKSUM(UnitsInStock))

FROM     Products

Output

7913472

Above example displays checksum to detect changes in the unit in stock field of product table.