Issue with sequence.currval in INSERT ALL...

Question

Hi Gurus,
I am having an issue with using sequence.currval in INSERT ALL with WHEN clause.Please check following example
Let say I have 4 tables
1) SOURCE_PARENT
PARENT_ID
========
10
20
2) SOURCE_CHILD
PARENT_ID CHILD_ID
========= ========
10     1
10     2
20     1
20     2
Now i have another 2 tables same as above definition(DEST_PARENT, DEST_CHILD),which i want to populate with above source data with new parent_id's from a sequence.
So I have used INSERT ALL as follows.
=====================================================
INSERT ALL
WHEN (prev_parent_id = 0)THEN
INTO dest_parent
values(test_s.nextval)
when 1 = 1 then
INTO dest_child
values(test_s.currval,child_id)
select
p.parent_id
,c.child_id
,LAG(c.parent_id, 1, 0) OVER (PARTITION BY c.parent_id ORDER BY c.child_id) prev_parent_id
from
source_parent p
,source_child c
where
p.parent_id = c.parent_id
order by p.parent_id
========================================================
Above INSERT ALL created following rows in DEST tables
1) DEST_PARENT
PARENT_ID
=========
75
77
2)DEST_CHILD
PARENT_ID CHILD_ID
========= =======
75     1
76     2 --- this should be same as above record
77     1
78     2 --this should be same as above record
As you can see test_s.nextval is executed 4 times even we do have WHEN Clause in INSERT ALL
Can you please check what's wrong in this INSERT ALL statement?
(or)
Any otherway of doing these INSERTS in a single SQL statement?
Any help would be appreciated!!
Thanks
srinivas.L

Answer 1

Sorry, but this solution does not work. I had to remove the constraints on the two tables dest_parent and dest_child just to show you, how bad your solution is
SQL> select * from source_parent;
PARENT_ID
        10
        20
2 rows selected.
SQL> select * from source_child;
PARENT_ID   CHILD_ID
        10          1
        10          2
        20          1
        20          2
        20          3
5 rows selected.
SQL> select * from dest_parent;
no rows selected
SQL> select * from dest_child;
no rows selected
SQL> insert all when
  2       (PREV_PARENT_ID = 0) then into DEST_PARENT
  3  values
  4       (TEST_S.nextval) when 1 = 1 then into DEST_CHILD
  5  values
  6       (case when PREV_PARENT_ID != 0 then TEST_S.currval - 1 else TEST_S.currval end,
  7        CHILD_ID)
  8       select P.PARENT_ID,
  9              C.CHILD_ID,
10              LAG(C.PARENT_ID, 1, 0) OVER(partition by C.PARENT_ID order by C.CHILD_ID) PREV_PARENT_ID
11       from SOURCE_PARENT P, SOURCE_CHILD C
12       where P.PARENT_ID = C.PARENT_ID
13       order by P.PARENT_ID
14  /
7 rows created.
SQL> select * from dest_parent;
PARENT_ID
        23
        26
2 rows selected.
SQL> select * from dest_child;
PARENT_ID   CHILD_ID
        21          2   -- ??? !!!
        23          1
        23          2
        24          3   -- !!!
        26          1
5 rows selected.
SQL>