with Dirs(id, parent, name) as (
  select 1, null, 'root1' from dual union all
  select 2, null, 'root2' from dual union all
  select 3, 1, 'dir1' from dual union all
  select 4, 3, 'subdir1' from dual union all
  select 5, 2, 'dir2' from dual),
Files(id, dir, name) as (
  select 1, 4, 'file1' from dual union all
  select 2, 6, 'file2' from dual),
Tree(id, parent, name, path) as(
  select id, dir, name, null from Files where id in (1/*, ... входной список*/)
 union all
  select Dirs.id, Dirs.parent, Dirs.name, Dirs.name||'\'||Tree.Path from Dirs, Tree
   where Dirs.id = Tree.parent)
select * from Tree

1     4     file1     /*тут пусто а хочу полный путь*/
4     3     subdir1   subdir1\
3     1     dir1      dir1\subdir1\
1           root1     root1\dir1\subdir1\ /*это полный путь*/

select d.*, sys_connect_by_path(name, '\') 
  from Dirs d
 start with id in (select dir from Files)
connect by prior parent = id