Auto-Increment a String of data

Question

OK, I see to be going round and round with the same problem.
I have UDF that contains 12 digits but the first 6 digits will always be the same.
The next 5 digits are the set of digits I need to auto increment
The last digit is a check digit that is pre-determined.
So I need assistance on a formatted search that looks at just the 5 digits and auto-increments those.
What seems to be the problems is once the UPC gets 12 digits, it only seems to start auto updating the 12 check digit and I do not want the 12th digit even touched.
I started out with 84573410001
After I made a update to that number the final value of the UDF is 845734100011
When a user used the formatted search the next value it should update is 84573410002
This is the query I got from teh forum a few days ago and it works as long as there is only 11 digits in the UDF, once I add teh 12th digit then it starts to auto increment the 12th digit.
Thanks,
Craig

Answer 1

That was the posting I did the first time around and the Query of:
SELECT str(CAST(MAX(T.U_UPC) as numeric)+1,12)
FROM RDR1 T
Works great when there is only 11 digits to increment but I want to only auto-increment a string of 5 digits with in the value.
First String (Will always be the same) 845734
Second String (THIS IS THE SET OF DIGITS I WANT TO AUTO_INCREMENT) Starts at 10001 and goes up.
Third string - 1 digit that is updated based on a set of values I built into a User Defined table and adds to the first 2 strings based on a comparison.