Query using system parameter LEVEL returns incorrect huge number of records

Question

We migrate our database from Oracle *9.2.0.6* to *11.2.0.1*
The query below throws "ORA-01788: CONNECT BY clause required in this query block".
select * from (
+select a.BOARD_ID, code, description, is_displayable, order_seq,  board_parent_id, short_description, IS_SUB_BOARD_DISPLAYABLE, <font color=blue>LEVEL</font> child_level, sp_board.get_parent_id(a.board_id) top_parent_id, is_top_selected isTopSelected+
from boards a, ALERT_MESSAGE_BOARD_TARGETS b
where a.board_id = b.board_id and is_displayable = 'Y' and alert_message_id = 5202) temp
start with board_parent_id = 0
connect by prior board_id = board_parent_id
ORDER SIBLINGS BY order_seq;
Based from online resources we modified "*_allow_level_without_connect_by*" by executing the statement.
alter system set "_allow_level_without_connect_by"=true scope=spfile;
After performing the above, ORA-01788 is resolved.
The new issue is that the same query above returns *9,015,853 records in 11g* but in *9i it returns 64 records*. 9i returns the correct number of records. And the cause for 11g returning greater number of records is due to system parameter <font color=blue>LEVEL</font> used in the query.
Why 11g is returning an incorrect huge number of records?
Any assistance to address this is greatly appreciated. Thanks!

Answer 1

The problem lies in th query.
Oracle <font color=blue>LEVEL</font> should not be used inside a subquery. After <font color=blue>LEVEL</font> is moved in the main query, the number of returned records is the same as in 9i.
select c.BOARD_ID, c.code, c.description, c.is_displayable, c.order_seq, c.board_parent_id, c.short_description, c.IS_SUB_BOARD_DISPLAYABLE, <font color=blue>LEVEL</font> child_level, c.top_parent_id, c.isTopSelected
from (
select a.BOARD_ID, code, description, is_displayable, order_seq, board_parent_id, short_description, IS_SUB_BOARD_DISPLAYABLE, sp_board.get_parent_id(a.board_id) top_parent_id, is_top_selected isTopSelected
from boards a, ALERT_MESSAGE_BOARD_TARGETS b
where a.board_id = b.board_id and is_displayable = 'Y' and alert_message_id = 5202
) c
start with c.board_parent_id = 0
connect by prior c.board_id = c.board_parent_id
ORDER SIBLINGS BY c.order_seq