hash join驱动表问题

explain plan for select c.oper_no, a.passbook_no, g.acct_no  
   from auto_savb_acct  g,
        auto_savb_acct  a,  
        (select * from comc_branch where substr(ctrl_bit,7,1)='0' )b,  
        auto_comc_clerk c,  
        comc_clerk_post d         
  where a.media_type = '3'  
    and substr(a.draw_mode, 1, 1) = '1'  
    and substr(a.status, 1, 1) = '0'  
    and g.media_type = '1'  
    and a.flag = '0'  
    and g.flag = '0'  
    and c.flag = '0'  
    and a.cur_code = 1  
    and g.cur_code = 1  
    and g.open_bran_code = c.bran_code  
    and a.open_bran_code = c.bran_code 
    and substr(g.status, 1, 1) = '0'  
    and c.post_no = d.post_no  
    and d.trans_code = '104106'  
    and c.bran_code=b.bran_code  
    and rownum < 2 ;
    
    select * from table(dbms_xplan.display());


 
Plan hash value: 3242562701
 
--------------------------------------------------------------------------------------------------
| Id  | Operation                      | Name            | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT               |                 |     1 |   187 |  1593   (1)| 00:00:20 |
|*  1 |  COUNT STOPKEY                 |                 |       |       |            |          |
|   2 |   NESTED LOOPS                 |                 |     1 |   187 |  1593   (1)| 00:00:20 |
|   3 |    NESTED LOOPS                |                 |     1 |   175 |  1593   (1)| 00:00:20 |
|*  4 |     HASH JOIN                  |                 |     3 |   429 |  1590   (1)| 00:00:20 |
|*  5 |      HASH JOIN                 |                 |     7 |   616 |   800   (1)| 00:00:10 |
|*  6 |       TABLE ACCESS FULL        | AUTO_SAVB_ACCT  |     1 |    57 |   790   (1)| 00:00:10 |
|*  7 |       TABLE ACCESS FULL        | AUTO_COMC_CLERK |   814 | 25234 |     9   (0)| 00:00:01 |
|*  8 |      TABLE ACCESS FULL         | AUTO_SAVB_ACCT  |    31 |  1705 |   790   (1)| 00:00:10 |
|*  9 |     TABLE ACCESS BY INDEX ROWID| COMC_BRANCH     |     1 |    32 |     1   (0)| 00:00:01 |
|* 10 |      INDEX UNIQUE SCAN         | BRAN_IDX        |     1 |       |     0   (0)| 00:00:01 |
|* 11 |    INDEX UNIQUE SCAN           | POST_IDX        |     1 |    12 |     0   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------------
 
Predicate Information (identified by operation id):
---------------------------------------------------
 
   1 - filter(ROWNUM<2)
   4 - access("G"."OPEN_BRAN_CODE"="C"."BRAN_CODE")
   5 - access("A"."OPEN_BRAN_CODE"="C"."BRAN_CODE")
   6 - filter(SUBSTR("A"."DRAW_MODE",1,1)='1' AND SUBSTR("A"."STATUS",1,1)='0' AND 
              "A"."MEDIA_TYPE"='3' AND "A"."CUR_CODE"=1 AND "A"."FLAG"='0')
   7 - filter("C"."FLAG"='0')
   8 - filter(SUBSTR("G"."STATUS",1,1)='0' AND "G"."MEDIA_TYPE"='1' AND "G"."CUR_CODE"=1 
              AND "G"."FLAG"='0')
   9 - filter(SUBSTR("CTRL_BIT",7,1)='0')
  10 - access("C"."BRAN_CODE"="COMC_BRANCH"."BRAN_CODE")
  11 - access("D"."POST_NO"=TO_NUMBER("C"."POST_NO") AND "D"."TRANS_CODE"='104106')

select count(*) from AUTO_SAVB_ACCT where SUBSTR("A"."DRAW_MODE",1,1)='1' AND SUBSTR("A"."STATUS",1,1)='0' AND 
              "A"."MEDIA_TYPE"='3' AND "A"."CUR_CODE"=1 AND "A"."FLAG"='0')
--4917

SQL> select count(*) from AUTO_SAVB_ACCT ;

  COUNT(*)
----------
     52132

SQL> select count(*) from AUTO_COMC_CLERK ;

  COUNT(*)
----------
       848


此时HASH JOIN的驱动表为AUTO_SAVB_ACCT,这个相比被驱动表AUTO_COMC_CLERK体积大,交换驱动表后

explain plan for select /*+ leading(c) */ c.oper_no, a.passbook_no, g.acct_no  
   from auto_savb_acct  g,
        auto_savb_acct  a,  
        (select * from comc_branch where substr(ctrl_bit,7,1)='0' )b,  
        auto_comc_clerk c,  
        comc_clerk_post d         
  where a.media_type = '3'  
    and substr(a.draw_mode, 1, 1) = '1'  
    and substr(a.status, 1, 1) = '0'  
    and g.media_type = '1'  
    and a.flag = '0'  
    and g.flag = '0'  
    and c.flag = '0'  
    and a.cur_code = 1  
    and g.cur_code = 1  
    and g.open_bran_code = c.bran_code  
    and a.open_bran_code = c.bran_code 
    and substr(g.status, 1, 1) = '0'  
    and c.post_no = d.post_no  
    and d.trans_code = '104106'  
    and c.bran_code=b.bran_code  
    and rownum < 2 ;

Plan hash value: 2775533374
 
--------------------------------------------------------------------------------------------------
| Id  | Operation                      | Name            | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT               |                 |     1 |   187 |  1593   (1)| 00:00:20 |
|*  1 |  COUNT STOPKEY                 |                 |       |       |            |          |
|   2 |   NESTED LOOPS                 |                 |     1 |   187 |  1593   (1)| 00:00:20 |
|   3 |    NESTED LOOPS                |                 |     1 |   175 |  1593   (1)| 00:00:20 |
|*  4 |     HASH JOIN                  |                 |     3 |   429 |  1590   (1)| 00:00:20 |
|*  5 |      HASH JOIN                 |                 |     7 |   616 |   800   (1)| 00:00:10 |
|*  6 |       TABLE ACCESS FULL        | AUTO_COMC_CLERK |   814 | 25234 |     9   (0)| 00:00:01 |
|*  7 |       TABLE ACCESS FULL        | AUTO_SAVB_ACCT  |     1 |    57 |   790   (1)| 00:00:10 |
|*  8 |      TABLE ACCESS FULL         | AUTO_SAVB_ACCT  |    33 |  1815 |   790   (1)| 00:00:10 |
|*  9 |     TABLE ACCESS BY INDEX ROWID| COMC_BRANCH     |     1 |    32 |     1   (0)| 00:00:01 |
|* 10 |      INDEX UNIQUE SCAN         | BRAN_IDX        |     1 |       |     0   (0)| 00:00:01 |
|* 11 |    INDEX UNIQUE SCAN           | POST_IDX        |     1 |    12 |     0   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------------
 
Predicate Information (identified by operation id):
---------------------------------------------------
 
   1 - filter(ROWNUM<2)
   4 - access("G"."OPEN_BRAN_CODE"="C"."BRAN_CODE")
   5 - access("A"."OPEN_BRAN_CODE"="C"."BRAN_CODE")
   6 - filter("C"."FLAG"='0')
   7 - filter(SUBSTR("A"."DRAW_MODE",1,1)='1' AND SUBSTR("A"."STATUS",1,1)='0' AND 
              "A"."MEDIA_TYPE"='3' AND "A"."CUR_CODE"=1 AND "A"."FLAG"='0')
   8 - filter(SUBSTR("G"."STATUS",1,1)='0' AND "G"."MEDIA_TYPE"='1' AND "G"."CUR_CODE"=1 
              AND "G"."FLAG"='0')
   9 - filter(SUBSTR("CTRL_BIT",7,1)='0')
  10 - access("C"."BRAN_CODE"="COMC_BRANCH"."BRAN_CODE")
  11 - access("D"."POST_NO"=TO_NUMBER("C"."POST_NO") AND "D"."TRANS_CODE"='104106')