You made the mistake of using ISNUMERIC to check for digits. ISNUMERIC does not equal ISALLDIGITS... try this and see what I mean...

SELECT dbo.check_digit('072---326')

Rather than just have it return a check digit, why not have it validate the ABA routing number altogether? For example...

[font="Courier New"]DECLARE @RoutingNumber VARCHAR(8000) --Allows check of wrong size numbers

    SET @RoutingNumber = '067803457'

SELECT CASE

        WHEN LEN(@RoutingNumber)=9

         AND @RoutingNumber NOT LIKE '%[^0-9]%' --Check to make sure is all digits

         AND RIGHT(@RoutingNumber ,1)

           = (--==== Calculates check digit (Digit 9)

              SELECT 10-SUM(mv.DigitVal)%10 --Sum of individual digit values subtracted for new number ending in 0

                FROM (--==== Gets multiplied value for each digit in 3, 7, 1 pattern

                      SELECT CASE

                             WHEN (t.N-1)%3 = 0 THEN SUBSTRING(@RoutingNumber,t.N,1)*3 --Digits 1,4,7

                             WHEN (t.N-1)%3 = 1 THEN SUBSTRING(@RoutingNumber,t.N,1)*7 --Digits 2,5,8

                             WHEN (t.N-1)%3 = 2 THEN SUBSTRING(@RoutingNumber,t.N,1)*1 --Digits 3,6

                             END AS DigitVal

                        FROM dbo.Tally t --See http://www.sqlservercentral.com/scripts/Advanced+SQL/62486/

                       WHERE t.N <= 8

                     ) mv

             )

        THEN 'Valid'

        ELSE 'Not Valid'

        END

go

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