Interview Question : Adding Each character of a number in a table

CREATE TABLE addnum ( id INT identity(1, 1) ,
                             val INT )
INSERT INTO addnum
SELECT ABS(CAST(NEWID() AS BINARY (6)) % 1000) + 1 randomNumber GO 1000
SELECT *
FROM addnum

;

WITH cte AS
  (SELECT id,
          cast(val AS varchar(10)) val,
          len(val) leng
   FROM addnum),
     cte1 AS
  (SELECT substring(val,1,1) x,
          id,
          1 num
   FROM cte
   UNION ALL SELECT Isnull(substring(cte.val,num+1,1),'0'),
                    cte.id,
                    num+1
   FROM cte1
   JOIN cte ON cte1.id=cte.id
   AND cte1.num<cte.leng)
SELECT cte.val,
       cte.id,
       sum(cast(x AS int)) addition
FROM cte1
JOIN cte ON cte.id=cte1.id
GROUP BY cte.val,
         cte.id
ORDER BY id