![]() Your calculation of (Doubled/10)+(Doubled-10) seems unnecessary to me. Your use of this function in a stored procedure has been a big boost to my knowledge (even though I don't yet understand how you did it) Stlll relvatively new to SQL after many years in MS Access and VBA, but always wanted to take it to te next level. Really gave me a breakthrough with one of the data integrity issues I was struggling with and will put this to good use in the future. RETURN is a test script that you can use: finally, sum the Summed column and if the result % 10 = 0, it's valid Luckily SQL Server butchers int division. WHEN Doubled IS NOT NULL AND Doubled = 10 now if the doubled digit is > 9, sum the digits, else carry forward UPDATE Doubled = CAST(ThisChar AS TINYINT) * 2 IF ( SELECT MAX(Position) % 2 FROM ) = 0 - evens double it and store the result in the Doubled column It includes the following functions: check (cc) - returns True if a given cc string is passes mod10, False otherwise. This script is (for instance) intended for people doing data validation for e-commerce applications. now for every 2nd digit from the right of the numeric, This is a small python script that contains logic for checking or generating valid (or invalid) credit card numbers. INNER JOIN t2 ON t1.Position = t2.OldPosition unfortunately this messes up the Position indicator, set up our table for algorithm calculation checking credit card numbers, make it 13 digits you can change this to any arbitrary amount, i.e. first a quick check to ensure we have at least 3 numbers in the string. Outputs: TINYINT: 2 = an error occurred, validity undetermined Function to calculate whether a number is valid according to the 'MOD 10' ![]() ![]() We could have also achieved this with a WHILE loop instead, but this way is also valid and a loop hardly seems worthwhile for 20 characters.ĬREATE FUNCTION dbo.usp_LuhnsAlgorithm_New ( VARCHAR(20) ) this avoids RBAR substringing each char to a table in a cursor we can then process the string as a set with a known number of elements convert the to a fixed width char datatype Let's now set up the function header, and put in a couple of simple constraints - the function can accept a string no longer than 20 characters, and if there aren't at least three digits present in the string, return an error code: Luckily we can combine this and use a temporary table variable both for cleansing the number and for validity checking. In the real world, we'll receive a number for testing as a string, or VARCHAR of indeterminate length, so we'll work on this basis rather than using an INT/BIGINT. We must also cleanse the card number and make sure we don't have any trailing spaces. What we CAN do, however, is use a temporary table variable to the same effect. So whereas in Python or C we might implement the card number as an array of numbers then apply transformations to all elements of the array, we don't have that luxury in SQL Server. The code we write must be fairly efficient, but we're constrained in a unique way by using T-SQL - we're writing in the language of relational set theory, not in object oriented language. Let's now turn our attention to rewriting this in T-SQL. The number we will use is an AMEX sample card number: Let's first get a number which we are testing for validity and split it out into its component digits, in a format we can easily understand. Stage 1: N * 2 for every 2nd N from the right All stages are carried out using simple mathematics and rules. The algorithm can be broken down into 4 stages. The samples are from PayPal and may be found here: Algorithm Overview One final note - any card numbers used here for illustration / example are fictitious - these pass the MOD 10 check, but are not real credit card numbers, only samples. I will also show you a method to remove 'noise' from the number - for example, spaces or leading/trailing characters. In the following sections I will provide a step-by-step guide to validating these numbers by hand, then show how we can replicate this as a User-Defined Function (UDF) within SQL Server. In the Next Steps section at the end of this tip. Luhn's Algorithm, links for which are provided It has no cryptographic validity, but it is a useful rule-of-thumb check that can be used to validate that a card number is correct, and can be used in its opposite form to generate account (and credit card) numbers - to help discourage potential fraudsters, this function is NOT covered here. Further help/ guidance will be greatly appreciated.The industry standard for checking credit card numbers for validity is known in colloquial terms as the 'MOD 10 Check', or more formally as Luhn's Algorithm. 2nd one I'm getting is object of type '_io.TextIOWrapper' has no len(). I wrote most of the code, but I'm stuck with 2 errors I get 1st one is num is referenced before assignment. I'm a beginner Python learner and I'm currently working on Luhn Algorithm to check credit card validation.
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