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SQL function to verify 'Check Digit' of given VISA/Master Card

, 23 Oct 2010 CPOL
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It help's to verify if the card number provided by the user is valid or not.
Hi,
 
Normally, every Visa/Master card have the 16 digits number printed(embossed) on the card. Last 16th digit is called as check digit.
 
There is an algorithm called MOD10 to verify that card number is valid or not. Here I am providing a link for detailed description about check digits logic: Cards Check Digits[^]
 
I am providing a SQL Server function for 'Check Digit' for Visa/Master Cards(16 Digits).
-- About using function: Pass the first 15 digits of the card no to the function 
-- and function will retuns the last check digit. 
-- That returned value should match with user provided 16th digit.

CREATE FUNCTION [DBO].[MOD10CHECKDIGIT](@STR VARCHAR(15))
RETURNS VARCHAR(1)
WITH EXECUTE AS CALLER
AS
BEGIN
DECLARE @RETURNSTR VARCHAR(100);
DECLARE @REVERSESTR VARCHAR(15);
DECLARE @CNT INT;
DECLARE @SUMVAL INT;
DECLARE @TEMPVAL INT;
DECLARE @TEMPVAL1 INT;
IF(LEN(@STR)<>15)
   SET @RETURNSTR='NO';
ELSE
  BEGIN
    SET @REVERSESTR = REVERSE(@STR);
    SET @SUMVAL=0;
    SET @CNT=1;
     WHILE @CNT < 16
      BEGIN
       SET @TEMPVAL =0;
       SET @TEMPVAL1 =0;
       IF((@CNT%2)<>0)
           SET @TEMPVAL =  (CONVERT(INT,SUBSTRING(@REVERSESTR,@CNT,1) * 2));
       ELSE
           SET @TEMPVAL =  (CONVERT(INT,SUBSTRING(@REVERSESTR,@CNT,1)));
       IF(@TEMPVAL>9)
          BEGIN
                SET @TEMPVAL1 = CONVERT(INT,SUBSTRING(CONVERT(VARCHAR,@TEMPVAL),1,1)) +
                             CONVERT(INT,SUBSTRING(CONVERT(VARCHAR,@TEMPVAL),2,1));
                SET @TEMPVAL=@TEMPVAL1;
          END;
       SET @SUMVAL = @SUMVAL + @TEMPVAL;
       SET @CNT= @CNT + 1;
      END
     SET @RETURNSTR=CONVERT(VARCHAR,(10 - (@SUMVAL%10)));
     --SET @RETURNSTR=CONVERT(VARCHAR,@SUMVAL);
  END
RETURN @RETURNSTR;
END
 
Note: Every VISA card starts with digit "4" and Mastercard stats with "5".

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Rajesh Anuhya
Software Developer (Senior)
India India
No Biography provided

Comments and Discussions

 
GeneralReason for my vote of 3 Interesting exercise in T-SQL progra... PinmemberRod Kemp23-Oct-10 4:49 
GeneralThanks Sandeep.., i want some more help from u, to edit my a... PinmemberRajesh Puli23-Oct-10 2:17 
GeneralReason for my vote of 5 Ok..i Have to admit..This is great. ... PinmemberGPUToaster23-Oct-10 2:16 
GeneralEdited, Formatted and published! PinmvpSandeep Mewara23-Oct-10 1:55 
GeneralOk i will update in tip/trick PinmemberRajesh Puli23-Oct-10 0:01 
GeneralOk. Can you please add what is 'Check Digit(mod10)'? Can you... PinmvpSandeep Mewara22-Oct-10 23:35 

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