update tt_com
   set chavea = (select max(ven.chavea)
                   from tt_ven ven inner join tt_tra tra on tra.filive = ven.codfil
                                                        and tra.seqive = ven.sequen
                  where tra.filico = tt_com.codfil
                    and tra.seqico = tt_com.sequen)
 where tt_com.chavea is null
   and tt_com.flgest <> 'D'
   and exists (select 1 as ok
                 from tt_ico ico inner join tt_tra tra on tra.filico = ico.codfil
                                                      and tra.seqico = ico.sequen
                                                      and tra.numico = ico.numite
                where ico.codfil = tt_com.codfil
                  and ico.sequen = tt_com.sequen);