Yes... in my first attempt, that's what happens... did you try the second attempt? For your convenience, here it is again...

--===== This just creates demonstrable test data and is NOT part of the solution

SET NOCOUNT ON

DECLARE @TestData TABLE(String VARCHAR(10))

INSERT INTO @TestData (String)

SELECT 'A012' UNION ALL

SELECT 'A12' UNION ALL

SELECT '12' UNION ALL

SELECT '1' UNION ALL

SELECT 'AB12' UNION ALL

SELECT 'AB2' UNION ALL

SELECT 'A' UNION ALL

SELECT '' UNION ALL

SELECT 'A14' UNION ALL

SELECT 'B2' UNION ALL

SELECT 'OBT' UNION ALL

SELECT 'YH3' UNION ALL

SELECT 'XX'

--===== This is the solution for the known constraints on the data as posted

DECLARE @MaxWidth TINYINT

SET @MaxWidth = (SELECT MAX(LEN(String)) FROM @TestData)

SELECT Original = String,

Modified = LEFT(d.String,d.LastLetter)

+ RIGHT(

REPLICATE('0',@MaxWidth)

+ SUBSTRING(d.String,d.LastLetter+1,@MaxWidth)

, @MaxWidth-d.LastLetter)

FROM (--==== Derived table "d" finds the interface between letters/digits

SELECT String,

LastLetter = PATINDEX('%[a-z][0-9]%',String+'0')

FROM @TestData

)d