updating 1st 5 digit of a column value in sql
Something like this? If value consists of digits only, replace first 5 characters with 1s; else, do nothing.

SQL&gt; with test (col) as
  2    (select '999999999' from dual union all
  3     select '123456789' from dual union all
  4     select 'MIS'       from dual union all
  5     select 'ab12345cc' from dual
  6    )
  7  select col,
  8    case when regexp_like(col, '^\d+$') then 11111 || substr(col, 6)
  9         else col
 10    end result
 11  from test;

COL       RESULT
--------- ---------------------
999999999 111119999
123456789 111116789
MIS       MIS
ab12345cc ab12345cc

SQL&gt;