binary checksum or checksum table

Hi
What is binary checksum or checksum table and where can we use this.

Thanks
atwork2003Asked:
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Aneesh RetnakaranConnect With a Mentor Database AdministratorCommented:
Did u  check books online, there are few exampples given



A. Use BINARY_CHECKSUM to detect changes in the rows of a table.
This example uses BINARY_CHECKSUM to detect changes in a row of the Products table in the Northwind database.

/*Get the checksum value before the values in the specific rows (#13-15) are changed.*/
USE   Northwind
GO
CREATE   TABLE TableBC (ProductID int, bchecksum int)
INSERT   INTO TableBC
         SELECT   ProductID, BINARY_CHECKSUM(*)
         FROM      Products
/*TableBC contains a column of 77 checksum values corresponding to each row in the Products table.*/

--A large company bought products 13-15.
--The new company modified the products names and unit prices.
--Change the values of ProductsName and UnitPrice for rows 13, 14, and 15 of the Products table.*/
UPDATE   Products
SET   ProductName='Oishi Konbu', UnitPrice=5
WHERE   ProductName='Konbu'

UPDATE   Products
SET   ProductName='Oishi Tofu', UnitPrice=20
WHERE   ProductName='Tofu'

UPDATE   Products
SET   ProductName='Oishi Genen Shouyu', UnitPrice=12
WHERE   ProductName='Genen Shouyu'

--Determine the rows that have changed.
SELECT   ProductID
FROM      TableBC
WHERE   EXISTS   (
      SELECT   ProductID
      FROM      Products
      WHERE      Products.ProductID = TableBC.ProductID
      AND   BINARY_CHECKSUM(*) <> TableBC.bchecksum)

Here is the result set:

ProductID
13
14
15

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