SOLVED:
UPDATE mytable
SET num = ( SELECT num FROM
(
select id,
concat(data, cast(group_row_number as char)) as num
from
(
select id, data,
@num := if(@data = `data`, @num + 1, 1) as group_row_number,
@data := `data` as dummy
from
(
select id, data
from mytable, (SELECT @rn:=0) r
) x
order by data, id
) x order by id
) tempSort
WHERE mytable.ID = tempSort.ID );
Thks again @bluefeet!!
solved MySQL – Convert a duplicate value in an unique with an increment concatenation [closed]