CHECKSUM is a TSQL function that computes a hash value over a list of arguments.  The great thing about creating a hash value for a table is that it gives you a unique value to represent each row. 

When would you use the CHECKSUM Function?

An example of using a CHECKSUM is to store the unique value for the entire row in a column that can be used later for comparison.  This is useful in a condition where all of the rows in a table need to be compared to perform an UPDATE.

When would you use the CHECKSUM Transformation?

Now that you have a little background on what CHECKSUM is it’s time to learn how to use it in SSIS.  The CHECKSUM Transformation is not included by default in SSIS but it was developed by Konesans and can be downloaded from www.sqlis.com. 

Normally in a package that is required to check for changes in data every single column from the destination must be compared to the incoming source.  With the CHECKSUM Transform creating a unique value for each row you only have to compare one column and that’s your CHECKSUM Value.

Checksum != DestCheckSum

To configure the CHECKSUM Transform open the editor and check the columns that you want to have the hash value created for and give the output column a name.

This is a great tool and a big time saver when developing!