create table tblA (id varchar2(10));
create table tblB (idx number(5), id varchar2(10), val1 number(1));

insert into tblA values ('a');
insert into tblA values ('b');

insert into tblB values (1, 'a', 1);
insert into tblB values (2, 'a', 2);
insert into tblB values (3, 'a', 3);
insert into tblB values (4, 'b', 1);

SELECT
  FROM tblA a, tblB b
 WHERE a.id = b.id
GROUP BY a.id

SELECT a.id, SUBSTR(b.vals,-(LENGTH(vals)-10)) as vals
  FROM tblA a
     , (SELECT id, MAX(SUBSTR(LPAD(TO_CHAR(idx),10,'0'),-10)||TO_CHAR(val1)) as vals
          FROM tblB
         GROUP BY id
        ) b
 WHERE b.id = a.id