select distinct c.id, a.key, h.addr
from asset a, asset_house ah, house h, client_house ch, client c
where [link all the tables together]

select c.id, a.key, h.addr
from asset a, asset_house ah, house h, client_house ch, client c,
(select count(*), id from
(select distinct c.id, a.key, h.addr
from asset a, asset_house ah, house h, client_house ch, client c
where [link all the tables together])
group by id
having count(*) = 1
) sq
where sq.id = c.id
and [link all the tables together]

SQL> select empno, ename, deptno
  2  from (select e.*, count(*) over (partition by deptno) cnt
  3        from emp e)
  4  where cnt=1
  5  /
     EMPNO ENAME          DEPTNO
---------- ---------- ----------
      7839 KING               10

1 row selected.