Getting all the children of a specific individual (tree-based hierachy)

Question

I am currently trying to get every relation & childs of any specific place of a tree. The tables are the following :

TABLE ORGANISATION                      TABLE LINKS
| Orga_Name | Code  | DELETED |         | Code  | Dads_Code |  STT  |
| DR        | DR001 |  FALSE  |(root)   | DR001 |   Null    |   OK  |(root no dad snif)
| DSI       | DS001 |  FALSE  |         | DS001 |   DR001   |   OK  |
| DLE       | DL001 |  FALSE  |         | DL001 |   DR001   |   OK  |
| DMP       | DM001 |  FALSE  |         | DM001 |   DS001   |   OK  |
| TRS       | TR001 |  FALSE  |         | TR001 |   DM001   |   OK  |
| TRE       | TE001 |  TRUE   |         | TE001 |   DM001   |   NOK |
| TRC       | TC001 |  FALSE  |         | TE001 |   DM001   |   NOK |

If any row has either DELETED = TRUE or STT = NOK, it shouldnt be considered at all. (just like TRE and TRC in this example)

The perfect result would be like the following:

|  Code  |   PICK-ONE|  Path                     |
|  DS001 |   DR001   |  DS001/DR001              |
|  DL001 |   DR001   |  DL001/DR001              |
|  DM001 |   DR001   |  DM001/DS001/DR001        |
|  TR001 |   DR001   |  TR001/DM001/DS001/DR001  |
|  DM001 |   DS001   |  DM001/DS001              |
|  TR001 |   DS001   |  TR001/DM001/DS001        |
|  TR001 |   DM001   |  DM001/TR001              |

So I can select a code in 'PICK-ONE' and get all the (direct & indirect) children of it as a list. I have been trying to use CONNECT_BY_ROOT, here's the current code I am using :

    SELECT  Code, 
            CONNECT_BY_ROOT Code,
            LEVEL-1, 
            SYS_CONNECT_BY_PATH(Code, '/') "Path"--,STT

    FROM    (
            SELECT o1.*,a1.STT,o1.DELETED
            FROM ORGANISATION o1
            LEFT JOIN LINKS a1
            ON o1.Code=a1.Code
            AND DELETED = 'FALSE'
            )
    WHERE LEVEL > 0 AND STT like 'OK' 
    CONNECT BY PRIOR Code = Dads_Code;

I am getting results mostly from the root, and one of his (always the same) children. In my example, the result I get would be from DS001 and DR001. Some of the results are correct. sadly the analyze stops at 2 level maximum ,there are some duplicates , and also some path to itself results (with 0 as level).

I have been trying to change Level or path, or change some conditions, but I am unable to find the problem. I would be glad if you could help me!

Answer 1

Don't use CONNECT BY since it's mostly obsolete at this point. It was a good way of querying hierarchies back in the day where there wasn't anything standard.

Use a Recursive Common Table Expression (aka Recursive CTE) available in most databases as part of the SQL standard.

For example if you want to retrieve all children of DR001 , you can do:

with n (code, dads_code, lvl, path) as (
  select code, dads_code, 1, code from links where code = 'DR001'
  union all
  select l.code, l.dads_code, n.lvl + 1, n.path || '/' || l.code
    from links l
    join n on n.code = l.dads_code
    where l.stt <> 'NOK'
      and not exists (select 1 from organisation o 
                      where o.code = l.code and deleted = 'TRUE')
)
select code, dads_code, lvl, path from n