with t1 as (
    select 'app5' name , 'app4' producer from dual union all
    select 'app4' name , 'app3' producer from dual union all
    select 'app3' name , 'app2' producer from dual union all
    select 'app2' name , 'app1' producer from dual union all
    select 'app5' name , 'app3' producer from dual union all
    select 'app5' name , 'app2' producer from dual union all
    select 'app6' name , 'app1' producer from dual union all
    select 'app6' name , 'app2' producer from dual union all
    select 'app5' name , 'app1' producer from dual
)
, t2 as (select producer from t1 minus select name from t1)
select max(connect_by_root producer||sys_connect_by_path(name,'/')) keep (dense_rank first order by level desc) path
from t1
where connect_by_isleaf =1
connect by prior name = producer 
start with t1.producer in (select producer from t2)
--group by  case when connect_by_isleaf =1 then name end 
group by name --поскольку where connect_by_isleaf =1

with t1 as (
    select 'app9' name , 'app4' producer from dual union all
    select 'app5' name , 'app4' producer from dual union all
    select 'app4' name , 'app3' producer from dual union all
    select 'app5' name , 'app8' producer from dual union all
    select 'app8' name , 'app3' producer from dual union all
    select 'app3' name , 'app2' producer from dual union all
    select 'app2' name , 'app1' producer from dual union all
    select 'app3' name , 'app7' producer from dual union all
    select 'app7' name , 'app1' producer from dual union all
    select 'app5' name , 'app3' producer from dual union all
    select 'app5' name , 'app2' producer from dual union all
    select 'app6' name , 'app1' producer from dual union all
    select 'app6' name , 'app2' producer from dual union all
    select 'app5' name , 'app1' producer from dual
)
, t2 as (select producer from t1 minus select name from t1)
, t3 as (select connect_by_root producer||sys_connect_by_path(name,'/') path
              , level as lvl
              , max(level) over (partition by name )  as maxlvl
           from t1
          where connect_by_isleaf =1
        connect by prior name = producer 
          start with t1.producer in (select producer from t2))
select * from t3 where lvl = maxlvl