UPDATE t_com
   SET t_order = t_code
;

t_code 의 정보가 t_order에 들어가겠죠.
정렬순서가 중요해보이지않네요.


 

 
UPDATE t_com 
   SET t_order = replace(t_code ,'0','')

MERGE INTO t_com a
USING
(
SELECT t_group, t_code, t_name
     , ROW_NUMBER() OVER(PARTITION BY t_group ORDER BY t_code) t_order
  FROM t_com
) b
ON (a.t_group = b.t_group AND a.t_code = b.t_code)
WHEN MATCHED THEN
UPDATE SET t_order = b.t_order
WHEN NOT MATCHED THEN
INSERT VALUES(b.t_group, b.t_code, b.t_name, b.t_order
;