Query Uses Index in 8i but not in 9i

Question

I have simple query which runs good in Oracle 8i. It uses index ,if i use = or in clause.
Same query is not using Index in Oracle 9i,(We made the the optimizer as choose) . If i remove in clause and make it = ,it is using index
select * from DWFE_ELE_CAT_ACC_HISTORY
where udc_acct_num in (Select z.LAH_CURR_LDC_ACCT_NUM
from DWFE_LDC_ACCT_HISTORY B,DWFE_LDC_ACCT_HISTORY z
Where B.LAH_CURR_LDC_ACCT_NUM ='0382900397'
and B.cpa_prem_num = Z.cpa_prem_num );

Answer 1

Plan for Oracle 8i
Execution Plan
0 SELECT STATEMENT Optimizer=RULE
1 0 NESTED LOOPS
2 1 VIEW OF 'VW_NSO_1'
3 2 REMOTE* RSSCP_DB
LINK
4 1 TABLE ACCESS (BY INDEX ROWID) OF 'CAT_TRANS_HISTORY'
5 4 INDEX (RANGE SCAN) OF 'IDX3_CAT_TRANS_HISTORY' (NON-UN
IQUE)
3 SERIAL_FROM_REMOTE SELECT /*+ */ DISTINCT "A1"."LAH_CURR_LDC_AC
CT_NUM" FROM "RSSC"."LDC_ACCT_HISTOR
Statistics
0 recursive calls
0 db block gets
8 consistent gets
0 physical reads
0 redo size
7827 bytes sent via SQL*Net to client
316 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
6 rows processed
Plan for Oracle 9i
Execution Plan
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=12018 Card=67728 Byt
es=9752832)
1 0 HASH JOIN (Cost=12018 Card=67728 Bytes=9752832)
2 1 VIEW OF 'VW_NSO_1' (Cost=707 Card=17041 Bytes=238574)
3 2 REMOTE* RSSCP_DB
LINK
4 1 TABLE ACCESS (FULL) OF 'CAT_TRANS_HISTORY' (Cost=6204 Ca
rd=1905290 Bytes=247687700)
3 SERIAL_FROM_REMOTE SELECT /*+ */ "A1"."LAH_CURR_LDC_ACCT_NUM" F
ROM "RSSC"."LDC_ACCT_HISTORY" "A2","
Statistics
42 recursive calls
1 db block gets
41038 consistent gets
41010 physical reads
380 redo size
7833 bytes sent via SQL*Net to client
253 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
6 rows processed