Need help: CONNECT by PRIOR query in ora10g

Question

Hi All,
Recently we have migrated the DB from 9i to 10g.
we used to have many rule based queries in 9i
and all are changed based on 10g.
All the queries that have CONNECT BY PRIOR
conditions seems to behave in wrong manner.
( same query in 9i,fetches less number of records where as 10g there were many
rows displayed eventhough it was not selected in where clause.- as per business logic )
After changing the below parameter setting , the problem was solved.
can you tell wts the below setting would do? by doing so , ur again making 10g
to behave like 9i so that full benefit of 10g is not used ?
Alter session set “_optimizer_connect_by_cost_based”=false

Answer 1

Hi, try this:
WITH t AS (
SELECT 100 AS node_id, cast(NULL AS NUMBER) AS parent_node_id FROM dual UNION ALL
SELECT 101 AS node_id, 100 AS parent_node_id FROM dual UNION ALL
SELECT 102 AS node_id, 100 AS parent_node_id FROM dual UNION ALL
SELECT 1021 AS node_id, 102 AS parent_node_id FROM dual UNION ALL
SELECT 1022 AS node_id, 102 AS parent_node_id FROM dual UNION ALL
SELECT 10221 AS node_id, 1022 AS parent_node_id FROM dual UNION ALL
SELECT 10222 AS node_id, 1022 AS parent_node_id FROM dual
SELECT DISTINCT CONNECT_BY_ROOT parent_node_id AS ID, node_id AS id1
FROM t
CONNECT BY t.node_id = PRIOR parent_node_id
START WITH parent_node_id = 1022
ORDER BY 1, 2;