OracleSQL -> Sort View by three levels - sql

Question

I created the following View in my Oracle SQL Developer:
The Results are not sorted In the way I need them.
I need to sort the results like this:
So If you would draw it as a graph with a depth of three
It would look like this:
The Maximum level depth is three. I tried different approaches with select connect_by_root, but it does not work. ORDER BY Also does no work because of the tree structure of the data.
Does anyone have a tip for me ?

Answer 1

You could use a left join:
select t.*
from t left join
t tp
on tp.id = t.parent_id
order by coalesce(tp.parent_id, t.parent_id, t.id),
coalesce(t.parent_id, t.id),
t.id
This assumes that the parent ids are smaller than the id, which seems to be true for your data. It is not a necessary assumption, but it simplifies the logic.

Answer 2

With a LEFT self join and conditional sorting:
select t1.*
from tablename t1
left join tablename t2 on t2.id = t1.parent_id
order by coalesce(t2.parent_id, t1.parent_id, t1.id),
case when t1.parent_id is null then 0 else 1 end,
case when t2.parent_id is not null then t1.parent_id else t1.id end,
case when t2.parent_id is null then 0 else 1 end,
t1.id
See the demo.
Results:
> ID | PARENT_ID | LEVEL
> -----: | --------: | :--------
> 29101 | null | LVL_ONE
> 153799 | 29101 | LVL_TWO
> 153800 | 153799 | LVL_THREE
> 153801 | 153799 | LVL_THREE
> 153803 | 29101 | LVL_TWO
> 153804 | 153803 | LVL_THREE
> 153802 | null | LVL_ONE
> 153805 | 153802 | LVL_TWO
> 153806 | 153805 | LVL_THREE

Answer 3

If the view you have used is a hierarchial query, then you have an option to "order siblings by", i would suggest you use that
Here is an example
https://oracle-base.com/articles/misc/hierarchical-queries

Answer 4

drop table a1;
CREATE TABLE a1
as
SELECT 153804 as ID, 153803 as PARENT_ID
FROM DUAL
UNION ALL
SELECT 153801, 153799
FROM DUAL
UNION ALL
SELECT 153803, 29101
FROM DUAL
UNION ALL
SELECT 29101, NULL
FROM DUAL
UNION ALL
SELECT 153802, NULL
FROM DUAL
UNION ALL
SELECT 153805, 153802
FROM DUAL
UNION ALL
SELECT 153806, 153805
FROM DUAL
UNION ALL
SELECT 153800, 153799
FROM DUAL
UNION ALL
SELECT 153799, 29101
FROM DUAL
;
select id, parent_id, level, 'LEVEL_' || level as level_desc
from a1
start with parent_id is null
connect by parent_id = prior(id)
order siblings by id
;