Issue with performance tuning of a query

Question

Hi,
I have a query which is in the below format
select a.* from
(inline query) a,
(inline query b)
where a.id = b.id;
Now i want the inline query b to be executed first and then joined with a.
How can i achieve the same.
Let me know if more information is required.

Answer 1

h4. NO_MERGE - This will allow inline query executing first
h4. LEADING(b) and USE_NL(b a) - We want to make driving table as "b" and then nest loop with "a"
SELECT /*+ LEADING(b) USE_NL(b a) */ a.*
FROM   (SELECT /*+ NO_MERGE */ LEVEL ID FROM dual CONNECT BY LEVEL <= 100 ) a,
       (SELECT /*+ NO_MERGE */ LEVEL ID FROM dual CONNECT BY LEVEL <= 10  ) b
WHERE  a.id = b.id;
| Id  | Operation                      | Name | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT               |      |     1 |    26 |     4   (0)| 00:00:01 |
|   1 |  NESTED LOOPS                  |      |     1 |    26 |     4   (0)| 00:00:01 |
|   2 |   VIEW                         |      |     1 |    13 |     2   (0)| 00:00:01 |
|*  3 |    CONNECT BY WITHOUT FILTERING|      |       |       |            |          |
|   4 |     FAST DUAL                  |      |     1 |       |     2   (0)| 00:00:01 |
|*  5 |   VIEW                         |      |     1 |    13 |     2   (0)| 00:00:01 |
|*  6 |    CONNECT BY WITHOUT FILTERING|      |       |       |            |          |
|   7 |     FAST DUAL                  |      |     1 |       |     2   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   3 - filter(LEVEL<=10)
   5 - filter("A"."ID"="B"."ID")
   6 - filter(LEVEL<=100)
{code}