Question

I have the need to return tree like results from a single table. At the moment im using connect by and start with to ensure that all the correct results are returned.

select id,parent_id
     from myTable 
 connect by prior id = parent_id start with name = 'manager' 
     group by id, parent_id
 order by parent_id asc

However i want the results to return in tree structure. So each time a parent row is found its children rows will be displayed directly underneath it. Then move onto next parent and do the same

Expected results

  - Parent A
   - child a
   - child b 
  - Parent B
   - child c
   - child d 

Actual results

- Parent A 
- Parent B
- child a 
- child b 
- child c 
- child d

Is it possible to do this in oracle? My table uses a parent_id field to identify when a row has a parent. Every row also has a sort order, which is the order it should be sorted under its parent and a unique Id.

I’m using an Oracle DB

Answer 1

What you want is to use ORDER SIBLINGS BY. The query you have is ordering by the parent_id column which is overriding any hierarchical ordering.

The query below should do what you need it to do:

with my_hierarchy_data as (
  select 1 as id, null as parent_id, 'Manager' as name from dual union all
  select 2 as id, 1 as parent_id, 'parent 1' as name from dual union all
  select 3 as id, 1 as parent_id, 'parent 2' as name from dual union all
  select 4 as id, 2 as parent_id, 'child 1' as name from dual union all
  select 5 as id, 2 as parent_id, 'child 2' as name from dual union all
  select 6 as id, 3 as parent_id, 'child 3' as name from dual union all
  select 7 as id, 3 as parent_id, 'child 4' as name from dual 
)
select id, parent_id, lpad('- ', level * 2, ' ') || name as name
from my_hierarchy_data
connect by prior id = parent_id
start with name= 'Manager'
order siblings by parent_id asc