Oracle "connect by" - multiple hierarchies

Question

We're on Oracle 11g R1. Here's the code:

CREATE TABLE T1 (ID NUMBER, PARENT_ID NUMBER, LEFT_SIBLING_ID NUMBER);
INSERT INTO T1 VALUES (1,NULL,NULL);
INSERT INTO T1 VALUES (3,1,NULL);
INSERT INTO T1 VALUES (2,1,3);
INSERT INTO T1 VALUES (4,2,NULL);
INSERT INTO T1 VALUES (5,2,4);
INSERT INTO T1 VALUES (10,NULL,1);
INSERT INTO T1 VALUES (12,10,NULL);
INSERT INTO T1 VALUES (11,10,12);

What I would like the result to be is:

ID-Tree
1
    3
    2
        4
        5
10
    12
    11

The key here is that besides the usual PRIOR ID = PARENT_ID hierarchy, there is another hierarchy based on PRIOR ID = LEFT_SIBLING_ID. The children are sorted in the order of PRIOR ID = LEFT_SIBLING_ID. That is why the 3 is followed by 2, and the 12 by 11, etc. That order is important.

I've drawn a blank on how to do this.

Edit:

More rows to clearly illustrate the ordering problem:

CREATE TABLE T1 (ID NUMBER, PARENT_ID NUMBER, LEFT_SIBLING_ID NUMBER);
INSERT INTO T1 VALUES (1,NULL,10);
INSERT INTO T1 VALUES (3,1,NULL);
INSERT INTO T1 VALUES (2,1,3);
INSERT INTO T1 VALUES (4,2,NULL);
INSERT INTO T1 VALUES (5,2,4);
INSERT INTO T1 VALUES (10,NULL,NULL);
INSERT INTO T1 VALUES (12,10,NULL);
INSERT INTO T1 VALUES (7,10,12);
INSERT INTO T1 VALUES (11,10,7);
INSERT INTO T1 VALUES (6,1,2);
INSERT INTO T1 VALUES (13,1,6);
COMMIT;

The result of the query:

select substr('----------', 1, lvl*2-2) || to_char(id) id_tree
from
 (select SYS_CONNECT_BY_PATH(to_char(id,'009'), ':') sort_path, 
        left_sibling_id, id, parent_id, level lvl
 from t1 
 start with parent_id is null
 connect by prior id = parent_id) q
start with left_sibling_id is null
connect by prior id = left_sibling_id 
and coalesce(parent_id,id) = coalesce(parent_id,id)
order by case lvl when 1 then sort_path 
                  else substr(sort_path,1,length(sort_path)-4) end,
         level;

ID_TREE                                            
-------------------------------------------------- 
1                                                  
--3                                                
--2                                                
--6                                                
--13                                               
----4                                              
----5                                              
10                                                 
--12                                               
--7                                                
--11                                               

 11 rows selected

Though the siblings are ordered properly (except the top level), they are no longer immediately under their parent.

Answer 1

Finally!

I created a 'sort order' column called SIBLING_LEVEL below by doing a CONNECT BY on LEFT_SIBLING_ID. Then I joined that to the original table. Then on the result of that join did a straightforward CONNECT BY ORDER SIBLING BY. Seems a bit brute force to me, but it's all I could come up with.

SELECT ROWNUM, LPAD(' ', (LEVEL*2) - 1, '-') || ID AS HIERARCHY, PARENT_ID,
LEFT_SIBLING_ID, LEVEL AS PARENT_CHILD_LEVEL
from
(
SELECT A.ID, A.PARENT_ID, A.LEFT_SIBLING_ID, B.SIBLING_LEVEL
FROM
T1 A
,
(
SELECT ID, SUBSTR('----------', 1, LVL*2-2) || TO_CHAR(ID) ID_TREE,
LEVEL AS SIBLING_LEVEL
FROM
(SELECT SYS_CONNECT_BY_PATH(TO_CHAR(ID,'009'), ':') SORT_PATH, 
    LEFT_SIBLING_ID, ID, PARENT_ID, LEVEL LVL
 FROM T1 
 START WITH PARENT_ID IS NULL
 CONNECT BY PRIOR ID = PARENT_ID) Q
START WITH LEFT_SIBLING_ID IS NULL
CONNECT BY PRIOR ID = LEFT_SIBLING_ID) B
WHERE A.ID = B.ID
) C
START WITH C.PARENT_ID IS NULL
CONNECT BY PRIOR C.ID = C.PARENT_ID
ORDER SIBLINGS BY SIBLING_LEVEL;

http://sqlfiddle.com/#!4/fcd68/5/0