Hierarchy in oracle

Question

Dear expert
After so much digging around and studying I have been able to make some progress in understanding and utilizing hierarchy structures in oracle but I am not there unfortunately. I have the following sample data below
create table t1
  parent_id varchar2(200),
  child_id varchar2(200)
insert into t1
  (parent_id, child_id)
values
  ('P1', 'C1');
insert into t1
  (parent_id, child_id)
values
  ('P2', 'C2');
insert into t1
  (parent_id, child_id)
values
  ('C1', 'D1');
insert into t1
  (parent_id, child_id)
values
  ('D1', 'D2');
  insert into t1
  (parent_id, child_id)
values
  ('D1', 'D3');I can use this query below to get a parents child assuming it has only one child
select t.child_id
from t1 t
start with t.parent_id = 'D1'
connect by prior t.parent_id = t.child_id;but when if the parent has two children it crashes and returns so many unwanted info...Can any one help with that.
which is meant to get a child associated parents all the way to the last parent but it is not working.
Overall this is the output I want for D1
Child Path
D1 D1->C1->P1
also I should have an opportunity depending on the parameter to stop on one level if possible,
All help is appreciated. Thank you

Answer 1

Hi,
Thanks for posting the CREATE TABLE and INSERT statements; that really helps!
Don't forget to say which version of Oracle you're using. This is especially important with CONNECT BY queries, since every version since Oracle 7 has had significant improvements in this area. The queries below work in Oracle 10.1 (and up).
Here's one way:
SELECT     CONNECT_BY_ROOT     child_id          AS child
,     SYS_CONNECT_BY_PATH (parent_id, ' -> ')     AS path
FROM     t1
WHERE     CONNECT_BY_ISLEAF     = 1
START WITH     child_id     = 'D1'
CONNECT BY     child_id     = PRIOR parent_id
;or, if you really want 'D1' in the path:
WITH     got_root   AS
     SELECT     CONNECT_BY_ROOT     child_id          AS child
     ,     SYS_CONNECT_BY_PATH (parent_id, ' -> ')     AS path
     FROM     t1
     WHERE     CONNECT_BY_ISLEAF     = 1
     START WITH     child_id     = 'D1'
     CONNECT BY     child_id     = PRIOR parent_id
SELECT     child
,     child || path     AS path
FROM     got_root
;Output:
CHILD      PATH
D1         D1 -> C1 -> P1Unfortunately, you can't always use CONNECT_BY_ROOT in place of any other expression. In this case, an ORA-00932 error occurs if you try to do the || operation in the CONNECT BY query, but you can do it in a separate query.
user13328581 wrote:
... also I should have an opportunity depending on the parameter to stop on one level if possible,Sorry, I don't understand. Post the exact output you want, formatted, between \ tags.
You can include conditions like "AND LEVEL <= n" in the CONNECT BY clause.  If n=1, it might be bettter just to do a self-join, rather than CONNECT BY.
Edited by: Frank Kulash on May 13, 2011 10:31 AM
Corrected spelling