How to make an union on 2 joined tables without affecting the sum on the column?
Ok, I solve it like this:

select CANT.ID,CANT.CANT_VAL,CANT.COD_VAL,CANT.FK_ID_CHEST,CANT.C1,CANT.C2 
        from cant
    union
    select COL.FK_ID_COL_DMA,COL.CANT_VAL,COL.COD_VAL,CANT2.FK_ID_CHEST,0,0 
        from col 
            inner join cant2 on cant2.id=COL.FK_ID_COL_DMA


Thanks!