Db2 Developer-C 11.1

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create table relations (id int, parent int);
insert into relations values(0,NULL);
insert into relations values(1,0);
insert into relations values(2,1);
insert into relations values(3,1);
insert into relations values(4,3);
insert into relations values(5,0);
insert into relations values(6,5);
insert into relations values(7,5);
insert into relations values(8,6);
insert into relations values(9,7);
insert into relations values(10,0);
insert into relations values(11,1);
with
n (id, parent, lvl, ordering) as (
  select id, parent, 1, lpad(id, 3, '0') || lpad('', 30, ' ') from relations where parent is null
 union all
  select r.id, r.parent, n.lvl + 1, trim(n.ordering) || '/' || lpad(r.id, 3, '0')
  from n, relations r where r.parent = n.id
)
select id, lpad(parent, lvl * 2, ' ') as parent, lvl
from n
order by ordering;


ID
PARENT
LVL


0
null
1

1
   0
2

2
     1
3

3
     1
3

4
       3
4

11
     1
3

5
   0
2

6
     5
3

8
       6
4

7
     5
3

9
       7
4

10
   0
2