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Luhn Testing In T-SQL

Phil Factor shows us the Luhn algorithm, a quick test to determine if a credit card number is potentially valid:

There are many ways of doing it in SQL. (and Rosetta Code is a good place to view solutions in various other languages). I believe that Peter Larsson holds the record for the fastest calculation of the Luhn test for a sixteen-digit credit card, with this code. As it stands, it isn’t a general solution, but it can be modified for different lengths of bank card.

Phil has two interesting T-SQL functions in the code and wants to find more.