[작업전]                                                     [원하는결과값]

   id      tn_no     gu_no                  =>      id    tn_no    gu_no  

11              1            0                               11         1                1

12              1            0                               12          1               2

13              2            0                               13          2               1

14              2            0                              14          2                 2               

15             1            0                               15          1                3

16             2            0                               16          2                 3

gu_no 자리가 0 에서  tn_no    순서대로 번호를  부여할려고합니다

내가 초보라   tn_no 번호로 정렬해서  

  select * from  table  order by tn_no,id

해서  while 문을 사용해서   gu_no 번호를 update 해서 결과값을  얻었는데

속도가   오래걸려서요

update 문장하나로 해결할수있는 방법이 없나 해서요