create table oper (
id   integer not null primary key,
id_m integer,
dt   date,
f1   integer,
f2   integer,
f3   integer
);


insert into oper(id, id_m, dt, f1, f2, f3) values(3, 2, '11.07.2016', 31, 32, 33);
insert into oper(id, id_m, dt, f1, f2, f3) values(4, 3, '12.07.2016', 41, 42, 43);
insert into oper(id, id_m, dt, f1, f2, f3) values(1, 2, '01.05.2016', 11, 12, 13);
insert into oper(id, id_m, dt, f1, f2, f3) values(2, 3, '02.05.2016', 21, 22, 23);
insert into oper(id, id_m, dt, f1, f2, f3) values(5, 4, '01.07.2016', 51, 52, 53);
commit;

execute block
returns (
  id   integer,
  id_m integer,
  dt   date,
  f1   integer,
  f2   integer,
  f3   integer
)
as
begin
  for select id_m, max(dt)
    from oper
    group by id_m
    into :id_m, :dt
    do begin
         select first 1
           id,  f1, f2, f3
         from oper
         where (oper.id_m = :id_m) and (oper.dt = :dt)
         order by id desc -- если с одной датой встретится несколько записей, возьмем с максимальным ID
         into :id,  :f1, :f2, :f3;
         --
         suspend;
       end
end;