Renumber duplicates to make them unique

       Table "public.t"
 Column |  Type   | Modifiers
--------+---------+-----------
 code   | text    |
 grid   | integer |

The codigo column, although of type text, has a numeric sequence which has duplicates. The grid column is a unique sequence.

select * from t order by grid;
 code | grid
------+------
 1    |    1
 1    |    2
 1    |    3
 2    |    4
 2    |    5
 2    |    6
 3    |    7

The goal is to eliminate the duplicates in the code column to make it unique. The result should be similar to:

 code | grid
------+------
 1    |    1
 6    |    2
 4    |    3
 2    |    4
 7    |    5
 5    |    6
 3    |    7

The version is 8.2 (no window functions).

create table t (code text, grid integer);
insert into t values
 ('1',1),
 ('1',2),
 ('1',3),
 ('2',4),
 ('2',6),
 ('3',7),
 ('2',5);

This is the solution that worked.

drop sequence if exists s;
create temporary sequence s;
select setval('s', (select max(cast(code as integer)) m from t));

update t
set code = i
from (
    select code, grid, nextval('s') i
    from (
        select code, max(grid) grid
        from t
        group by code
        having count(*) > 1
        order by grid
    ) q
) s
where
    t.code = s.code
    and
    t.grid = s.grid

The problem with it is that the update command must be repeated until there are no more duplicates. It is just a "it is not perfect" problem as it is a one time operation only.