View is ignoring the hints

Question

I am using Oracle 10g R2.
I want to pass hints to a view but they are not being honoured.
CREATE VIEW V AS
     SELECT DT.UNIQUE_ID,
            DT.INFO_ID AS BATCH_REFERENCE,
            DT.INSTRUCTION_ID AS TR_REFERENCE,
            DT.TOTAL_TRANSACTION_NO AS NO_OF_TRANSACTIONS,
       FROM    MY_PAYMENT DT JOIN MY_STATUS ST
             ON DT.BATCH_STATUS = ST.STATUS;
Now when I run the below query, then hints are ignored. However if i pass the INDEX hint directly in the above SELECT in the view definition, then hints are honoured.
SELECT /*+ INDEX(V.DT) */ * FROM V
Can you help?

Answer 1

Moazzam wrote:
So what is the objective behind using a HINT to force an index scan?
Actually, the statistics gathering job takes more than 16 hours to complete. Due to which, most of the time, the plan generated are not optimized due to lack of up to date stats.
In that case trying to bypass the actual issue by using HINT does not look like a wise idea to me. Any ways you need to use GLOBAL HINT when using VIEW.
Oracle documented it in detail. You can read it here
http://docs.oracle.com/cd/B19306_01/server.102/b14211/hintsref.htm#i22065
Below is a simple example using EMP and DEPT table.
Following is the view
SQL> create view v
  2  as
  3  select d.dname, e.ename
  4    from emp e join dept d
  5      on e.deptno = d.deptno;
View created.
Now plan for the query with and without hint
SQL> explain plan for
  2  select e.ename, d.dname from emp e join dept d on e.deptno = d.deptno;
Explained.
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
Plan hash value: 14164142
| Id  | Operation                    | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT             |         |    11 |   242 |     4  (25)| 00:00:01 |
|   1 |  MERGE JOIN                  |         |    11 |   242 |     4  (25)| 00:00:01 |
|   2 |   TABLE ACCESS BY INDEX ROWID| DEPT    |     4 |    52 |     1   (0)| 00:00:01 |
|   3 |    INDEX FULL SCAN           | DEPT_PK |     4 |       |     1   (0)| 00:00:01 |
|*  4 |   SORT JOIN                  |         |    11 |    99 |     3  (34)| 00:00:01 |
|   5 |    TABLE ACCESS FULL         | EMP     |    11 |    99 |     2   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   4 - access("E"."DEPTNO"="D"."DEPTNO")
       filter("E"."DEPTNO"="D"."DEPTNO")
18 rows selected.
SQL> explain plan for
  2  select /*+ INDEX(e emp_pk) */ e.ename, d.dname from emp e join dept d on e.deptno = d.deptno;
Explained.
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
Plan hash value: 2399836226
| Id  | Operation                     | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT              |         |    11 |   242 |     3  (34)| 00:00:01 |
|   1 |  MERGE JOIN                   |         |    11 |   242 |     3  (34)| 00:00:01 |
|   2 |   TABLE ACCESS BY INDEX ROWID | DEPT    |     4 |    52 |     1   (0)| 00:00:01 |
|   3 |    INDEX FULL SCAN            | DEPT_PK |     4 |       |     1   (0)| 00:00:01 |
|*  4 |   SORT JOIN                   |         |    11 |    99 |     2  (50)| 00:00:01 |
|   5 |    TABLE ACCESS BY INDEX ROWID| EMP     |    11 |    99 |     1   (0)| 00:00:01 |
|   6 |     INDEX FULL SCAN           | EMP_PK  |    11 |       |     1   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   4 - access("E"."DEPTNO"="D"."DEPTNO")
       filter("E"."DEPTNO"="D"."DEPTNO")
19 rows selected.
Now plan for the query on view with and without hint
SQL> explain plan for
  2  select * from v;
Explained.
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
Plan hash value: 14164142
| Id  | Operation                    | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT             |         |    11 |   242 |     4  (25)| 00:00:01 |
|   1 |  MERGE JOIN                  |         |    11 |   242 |     4  (25)| 00:00:01 |
|   2 |   TABLE ACCESS BY INDEX ROWID| DEPT    |     4 |    52 |     1   (0)| 00:00:01 |
|   3 |    INDEX FULL SCAN           | DEPT_PK |     4 |       |     1   (0)| 00:00:01 |
|*  4 |   SORT JOIN                  |         |    11 |    99 |     3  (34)| 00:00:01 |
|   5 |    TABLE ACCESS FULL         | EMP     |    11 |    99 |     2   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   4 - access("E"."DEPTNO"="D"."DEPTNO")
       filter("E"."DEPTNO"="D"."DEPTNO")
18 rows selected.
Now we use GLOBAL TABLE HINT
SQL> explain plan for
  2  select /*+ INDEX(@SEL$2 e emp_pk) */ * from v;
Explained.
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
Plan hash value: 2399836226
| Id  | Operation                     | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT              |         |    11 |   242 |     3  (34)| 00:00:01 |
|   1 |  MERGE JOIN                   |         |    11 |   242 |     3  (34)| 00:00:01 |
|   2 |   TABLE ACCESS BY INDEX ROWID | DEPT    |     4 |    52 |     1   (0)| 00:00:01 |
|   3 |    INDEX FULL SCAN            | DEPT_PK |     4 |       |     1   (0)| 00:00:01 |
|*  4 |   SORT JOIN                   |         |    11 |    99 |     2  (50)| 00:00:01 |
|   5 |    TABLE ACCESS BY INDEX ROWID| EMP     |    11 |    99 |     1   (0)| 00:00:01 |
|   6 |     INDEX FULL SCAN           | EMP_PK  |    11 |       |     1   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   4 - access("E"."DEPTNO"="D"."DEPTNO")
       filter("E"."DEPTNO"="D"."DEPTNO")
19 rows selected.
SQL>