Recursive subquery

Question

I have a table with origin and destination ids.
There can be a dynamic number of connections ( not expecting more than 5) and the relation is always one to one: A -->B-->C-->D
A or B or C or D can only apear in a relation, This mean A-->C cannot happen because A e already connected to B.
I want to create a querie that receives the last destination values and return a column with the origin values that are related with that value:
for example:
if my parameter value is D, my result will be a column with three rows : A,B,C
if my parameter value is C, my result will be a column with two rows : A,B
example:
create table test_list as (
select 32000 origin, 68200 destination from dual
union all
select 60000 origin, 168200 destination from dual
union all
select 8200 origin, 36600 destination from dual
union all
select 36600 origin, 8400 destination from dual
union all
select 8400 origin, 61800 destination from dual
)I tried conect by prior and connect by root but could not achieve it!
found also some articles about "Recursive Subquery Factoring" but that got even worst because I could not get it to work.
My database is "Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production"
SELECT origin   from test_list  where
    origin in (select *  FROM (
     SELECT CONNECT_BY_ROOT destination
      FROM test_list
    CONNECT BY PRIOR origin = destination and destination =68200 )
)So in my list:
32000 connects to 68200
60000 connects to 168200
8200 connects to 36600
36600 connects to 8400
8400 connects to 61800
My expected results are:
If parameter "VALUE_TO_SEARCH" = 68200 I expect only: 32000
If parameter "VALUE_TO_SEARCH" = 168200 I expect only: 60000
If parameter "VALUE_TO_SEARCH" = 61800 I expect : 8400,36600,8200
If parameter "VALUE_TO_SEARCH" = 32000 I expect no results.
What should be the best method to use, for best performance and in case is with the CONNECT_BY_ROOT and " CONNECT BY PRIOR" what am I doing wrong there?
Best regards,
Ricardo Tomás

Answer 1

Use START WITH clause:
SQL> select * from test_list;
    ORIGIN DESTINATION
     32000       68200
     60000      168200
      8200       36600
     36600        8400
      8400       61800
SQL> select  origin
  2    from  test_list
  3    start with destination = &destination
  4    connect by destination = prior origin
  5  /
Enter value for destination: 68200
old   3:   start with destination = &destination
new   3:   start with destination = 68200
    ORIGIN
     32000
SQL> /
Enter value for destination: 168200
old   3:   start with destination = &destination
new   3:   start with destination = 168200
    ORIGIN
     60000
SQL> /
Enter value for destination: 61800
old   3:   start with destination = &destination
new   3:   start with destination = 61800
    ORIGIN
      8400
     36600
      8200
SQL> /
Enter value for destination: 32000
old   3:   start with destination = &destination
new   3:   start with destination = 32000
no rows selected
SQL> SY.