Hint in query

Question

ear friends,
my query is like below.
if you people see i have used Hint in the first query but still my tbl_bank_statement showing Full Table Scan.
pls. help if i want remove FTS on table what should i modify in below query.
SELECT /* index(tbl_bank_statement indx_policyno) +*/t1.policy_no AS policy_no, t1.request_no AS request_no,t1.ecs_mandate_status AS ecsmandatestatus ,t1.ecs_micr_code AS ecsmicrcode,t1.createddate  ,t1.userid,t1.ecs_account_no,
t1.ecs_micr_code,t1.Ecs_Factoring_House,t1.ecs_startdate,t1.ecs_enddate,REJECTIONREASON AS rejectionreason,
t1.ecs_first_account_holder_name,t1.ecs_second_account_holder_name,t1.ecs_mandate_ref_no,t1.ecs_trd_party_premium_payment
,t1.ecs_reln_btn_owner_payor,t1.ecs_account_type,NULL AS REQUESTDATE
FROM tbl_bank_statement t1
Where not exists( SELECT t3.serreqid FROM m_ps_otherdetails t3,t_ps_serreq_log ps
Where t3.policyno = t1.policy_no
and t3.serreqid =ps.serreqid
and ps.serreqtypeid in (37,38,39)
and t3.ECS_Mandate_status = ''4'')
UNION
SELECT t2.policyno AS policy_no,t2.serreqid AS request_no,t2.ecs_mandate_status AS ecsmandatestatus,t2.ecs_micr_code AS ecsmicrcode,t2.createddate,t2.createdby AS userid,t2.ecs_account_no,
t2.ecs_micr_code,t2.Ecs_Factoring_House,t2.ecs_startdate,t2.ecs_enddate,reqlog.rejectionreason,
2.ecs_first_account_holder_name,t2.ecs_second_account_holder_name,t2.ecs_mandate_ref_no,t2.ecs_trd_party_premium_payment,
t2.ecs_reln_btn_owner_payor,t2.ecs_account_type, reqlog.REQUESTDATE AS REQUESTDATE
FROM m_ps_otherdetails t2

Answer 1

Hints are directives. The only time I've EVER seen a hint ignored is if it creates a situation where it would invalidate the results, or there's a bug in the oracle code itself.
It will very much not ignore an index hint if it thinks a FTS is 'cheaper'.
mkr02@ORA11GMK> create table t as select level lvl from dual connect by level < 100000
  2  /
Table created.
Elapsed: 00:00:01.53
mkr02@ORA11GMK> alter table t modify lvl not null
  2  /
Table altered.
Elapsed: 00:00:00.83
mkr02@ORA11GMK> create index idx on t(lvl)
  2  /
Index created.
Elapsed: 00:00:00.43
mkr02@ORA11GMK> explain plan for select lvl from t
  2  /
Explained.
Elapsed: 00:00:00.25
mkr02@ORA11GMK> @xplan
PLAN_TABLE_OUTPUT
Plan hash value: 1601196873
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT  |      |   108K|  1380K|    47   (3)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| T    |   108K|  1380K|    47   (3)| 00:00:01 |
Note
   - dynamic sampling used for this statement (level=2)
12 rows selected.
Elapsed: 00:00:01.05
mkr02@ORA11GMK> explain plan for
  2  select /*+ index(t idx) */ lvl from t
  3  /
Explained.
Elapsed: 00:00:00.02
mkr02@ORA11GMK> @xplan
PLAN_TABLE_OUTPUT
Plan hash value: 2099009386
| Id  | Operation        | Name | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT |      |   108K|  1380K|   237   (1)| 00:00:03 |
|   1 |  INDEX FULL SCAN | IDX  |   108K|  1380K|   237   (1)| 00:00:03 |
Note
   - dynamic sampling used for this statement (level=2)
12 rows selected.
Elapsed: 00:00:00.06