Same Conect By query workds fine in 9i but not in 10g - Please help

Question

We recently moved our project from 9i to 10g. A connect by query works fine in 9i environment but same not working in 10g environment. Please help.
While trying with a sample table, that also behaves samem way. Please find the query and help on how to solve.
create table test_connect_by (
parent number,
child number,
constraint uq_tcb unique (child)
insert into test_connect_by values ( 5, 2);
insert into test_connect_by values ( 5, 3);
insert into test_connect_by values (18,11);
insert into test_connect_by values (18, 7);
insert into test_connect_by values (17, 9);
insert into test_connect_by values (17, 8);
insert into test_connect_by values (26,13);
insert into test_connect_by values (26, 1);
insert into test_connect_by values (26,12);
insert into test_connect_by values (15,10);
insert into test_connect_by values (15, 5);
insert into test_connect_by values (38,15);
insert into test_connect_by values (38,17);
insert into test_connect_by values (38, 6);
insert into test_connect_by values (null, 38);
insert into test_connect_by values (null, 26);
insert into test_connect_by values (null, 18);
COMMIT;
In Oracle 10g:
SQL> select level, lpad(' ',2*(level-1)) || to_char(child) s
2 from test_connect_by
3 start with level = 1
4 connect by prior child = parent;
no rows selected
In Oracle 9i:
SQL> select level, lpad(' ',2*(level-1)) || to_char(child) s
2 from test_connect_by
3 start with level = 1
4 connect by prior child = parent;
LEVEL S
1 2
1 3
1 10
1 5
2 2
2 3
1 9
1 8
1 11
1 7
1 13
1 1
1 12
1 15
2 10
2 5
3 2
3 3
1 17
2 9
2 8
1 6
1 38
2 15
3 10
3 5
4 2
4 3
2 17
3 9
3 8
2 6
1 26
2 13
2 1
2 12
1 18
2 11
2 7
39 rows selected.

Answer 1

Hi,
user10739895 wrote:
It works fine and gives result without the "START WITH LEVEL = 1".
However, in 9i, we get the result with the clause "START WITH LEVEL = 1" and after migrating, now in 10g, we are not getting the result. Is it like in 10g, if it is Level 1, we should not specify?
Also, please clarify, is it like, if we don't specify the default is Level 1? Conceptually, LEVEL is assigned when rows enter the result set. Rows that enter because of the START WITH clause, by definition, have LEVEL=1. Rows that enter because of CONNECT BY have the LEVEL of the row to which they are connected, plus 1.
"START WITH LEVEL = 1" returns no rows when I try it in Oracle 11.1.0.
I suggest not using it.
If you don't have a START WITH clause, you'll START WITH every row in the table. That seems to be what you got in Oracle 9. Is that what you want? If so, then just don't use a START WITH clause.