sort merge join,hash join,netsloop join

                                                Join Operations

? SORT-MERGE JOIN

– Sorts tables on the join key and then merges them together

– Sorts are expensive



? NESTED LOOPS

– Retrieves a row from one table and finds the corresponding rows in the other table

– Usually best for small numbers of rows



? HASH JOIN

– Build hash table in memory for smaller row source

– Hash larger row source

– Probe in-memory hash table for matches

– Hash joins are only considered by the CBO







SORT-MERGE JOIN

根据关联列排序2个表,然后再进行merge操作

当然排序是很昂贵的

无驱动表概念



支持不等值连接



嵌套循环:

Oracle从较小结果集(驱动表/外部表)中读取一行，然后和较大结果集(被探查表/内部表)中的所有数据逐条进行比较(嵌套循环可以用于非等值连接)，

如果符合规则，就放入结果集中，然后取较小结果集的下一条数据继续进行循环，直到结束。嵌套循环只适合输出少量结果集或者是用于快速输出结果集。





HASH JOIN

HASH JOIN 选择小表做驱动表，小表指的不是表的行数，而是指的是 行数*列宽度

HASH JOIN只能用于等值连接



把小的结果集(驱动表)来创建hash table



然后 HASH 大的结果集



探测内存里的Hash表来匹配:



实验SQL:

SELECT  a.cur_code,b.int_sub_code,b.plan_int_sub_code, a.acct_bran_code , sum(a.payable_int_amt)  as amt

   FROM comr_intdist a,savc_buscode b

   WHERE a.acct_flag = '1'

   AND a.bus_code = b.bus_code

   and a.LAST_MODI_DATE = '2013-12-31'

   AND ((a.term = b.term

   AND rtrim(a.sub_code) =rtrim(b.sub_code))

   or

   a.bus_code=77 )

   GROUP BY a.cur_code,b.int_sub_code, b.plan_int_sub_code,a.acct_bran_code

;



SORT-MERGE JOIN：



Execution Plan

----------------------------------------------------------

Plan hash value: 3181909998



----------------------------------------------------------------------------------------------

| Id  | Operation             | Name         | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |

----------------------------------------------------------------------------------------------

|   0 | SELECT STATEMENT      |              |  8117 |   539K|       | 20129   (2)| 00:04:02 |

|   1 |  HASH GROUP BY        |              |  8117 |   539K|       | 20129   (2)| 00:04:02 |

|   2 |   MERGE JOIN          |              |  8117 |   539K|       | 20127   (2)| 00:04:02 |

|   3 |    SORT JOIN          |              |   409 | 10634 |       |     6  (17)| 00:00:01 |

|   4 |     TABLE ACCESS FULL | SAVC_BUSCODE |   409 | 10634 |       |     5   (0)| 00:00:01 |

|*  5 |    FILTER             |              |       |       |       |            |          |

|*  6 |     SORT JOIN         |              |  1136K|    45M|   139M| 20077   (2)| 00:04:01 |

|*  7 |      TABLE ACCESS FULL| COMR_INTDIST |  1136K|    45M|       |  7704   (2)| 00:01:33 |

----------------------------------------------------------------------------------------------



Predicate Information (identified by operation id):

---------------------------------------------------



   5 - filter("A"."TERM"="B"."TERM" AND RTRIM("A"."SUB_CODE")=RTRIM("B"."SUB_CODE")

              OR "A"."BUS_CODE"=77)

   6 - access("A"."BUS_CODE"="B"."BUS_CODE")

       filter("A"."BUS_CODE"="B"."BUS_CODE")

   7 - filter("A"."ACCT_FLAG"='1' AND "A"."LAST_MODI_DATE"=TO_DATE(' 2013-12-31

              00:00:00', 'syyyy-mm-dd hh24:mi:ss'))





Statistics

----------------------------------------------------------

          1  recursive calls

          2  db block gets

      27016  consistent gets

      27000  physical reads

          0  redo size

      30923  bytes sent via SQL*Net to client

       1147  bytes received via SQL*Net from client

         59  SQL*Net roundtrips to/from client

          2  sorts (memory)

          0  sorts (disk)

        860  rows processed





查看表的访问次数；

Plan hash value: 3181909998



------------------------------------------------------------------------------------------------------------------------------------

| Id  | Operation             | Name         | Starts | E-Rows | A-Rows |   A-Time   | Buffers | Reads  |  OMem |  1Mem | Used-Mem |

------------------------------------------------------------------------------------------------------------------------------------

|   0 | SELECT STATEMENT      |              |      1 |        |    860 |00:00:07.55 |   27018 |  26880 |       |       |          |

|   1 |  HASH GROUP BY        |              |      1 |   8117 |    860 |00:00:07.55 |   27018 |  26880 |   835K|   835K| 1454K (0)|

|   2 |   MERGE JOIN          |              |      1 |   8117 |   1131K|00:00:07.01 |   27018 |  26880 |       |       |          |

|   3 |    SORT JOIN          |              |      1 |    409 |    409 |00:00:00.01 |      21 |      0 | 55296 | 55296 |49152  (0)|

|   4 |     TABLE ACCESS FULL | SAVC_BUSCODE |      1 |    409 |    409 |00:00:00.01 |      21 |      0 |       |       |          |

|*  5 |    FILTER             |              |    409 |        |   1131K|00:00:06.65 |   26997 |  26880 |       |       |          |

|*  6 |     SORT JOIN         |              |    409 |   1136K|   5241K|00:00:04.55 |   26997 |  26880 |    66M|  2830K|   59M (0)|

|*  7 |      TABLE ACCESS FULL| COMR_INTDIST |      1 |   1136K|   1138K|00:00:01.04 |   26997 |  26880 |       |       |          |

------------------------------------------------------------------------------------------------------------------------------------



Predicate Information (identified by operation id):

---------------------------------------------------



   5 - filter((("A"."TERM"="B"."TERM" AND RTRIM("A"."SUB_CODE")=RTRIM("B"."SUB_CODE")) OR "A"."BUS_CODE"=77))

   6 - access("A"."BUS_CODE"="B"."BUS_CODE")

       filter("A"."BUS_CODE"="B"."BUS_CODE")

   7 - filter(("A"."ACCT_FLAG"='1' AND "A"."LAST_MODI_DATE"=TO_DATE(' 2013-12-31 00:00:00', 'syyyy-mm-dd hh24:mi:ss')))





34 rows selected.



嵌套循环:



Execution Plan

----------------------------------------------------------

Plan hash value: 2053094138



---------------------------------------------------------------------------------------------------

| Id  | Operation                     | Name              | Rows  | Bytes | Cost (%CPU)| Time     |

---------------------------------------------------------------------------------------------------

|   0 | SELECT STATEMENT              |                   |  8117 |   539K|  2283K  (1)| 07:36:37 |

|   1 |  HASH GROUP BY                |                   |  8117 |   539K|  2283K  (1)| 07:36:37 |

|   2 |   NESTED LOOPS                |                   |       |       |            |          |

|   3 |    NESTED LOOPS               |                   |  8117 |   539K|  2283K  (1)| 07:36:37 |

|*  4 |     TABLE ACCESS FULL         | COMR_INTDIST      |  1136K|    45M|  7704   (2)| 00:01:33 |

|*  5 |     INDEX RANGE SCAN          | SAVC_BUSCODE_IDX1 |     5 |       |     1   (0)| 00:00:01 |

|*  6 |    TABLE ACCESS BY INDEX ROWID| SAVC_BUSCODE      |     1 |    26 |     2   (0)| 00:00:01 |

---------------------------------------------------------------------------------------------------



Predicate Information (identified by operation id):

---------------------------------------------------



   4 - filter("A"."ACCT_FLAG"='1' AND "A"."LAST_MODI_DATE"=TO_DATE(' 2013-12-31 00:00:00',

              'syyyy-mm-dd hh24:mi:ss'))

   5 - access("A"."BUS_CODE"="B"."BUS_CODE")

   6 - filter("A"."TERM"="B"."TERM" AND RTRIM("A"."SUB_CODE")=RTRIM("B"."SUB_CODE") OR

              "A"."BUS_CODE"=77)





Plan hash value: 2053094138



-------------------------------------------------------------------------------------------------------------------------------------------------

| Id  | Operation                     | Name              | Starts | E-Rows | A-Rows |   A-Time   | Buffers | Reads  |  OMem |  1Mem | Used-Mem |

-------------------------------------------------------------------------------------------------------------------------------------------------

|   0 | SELECT STATEMENT              |                   |      1 |        |    860 |00:00:16.87 |     290K|  26880 |       |       |          |

|   1 |  HASH GROUP BY                |                   |      1 |   8117 |    860 |00:00:16.87 |     290K|  26880 |   835K|   835K| 1456K (0)|

|   2 |   NESTED LOOPS                |                   |      1 |        |   1131K|00:00:15.90 |     290K|  26880 |       |       |          |

|   3 |    NESTED LOOPS               |                   |      1 |   8117 |   5241K|00:00:06.74 |   27132 |  26880 |       |       |          |

|*  4 |     TABLE ACCESS FULL         | COMR_INTDIST      |      1 |   1136K|   1138K|00:00:00.88 |   26997 |  26880 |       |       |          |

|*  5 |     INDEX RANGE SCAN          | SAVC_BUSCODE_IDX1 |   1138K|      5 |   5241K|00:00:03.59 |     135 |      0 |       |       |          |

|*  6 |    TABLE ACCESS BY INDEX ROWID| SAVC_BUSCODE      |   5241K|      1 |   1131K|00:00:06.08 |     262K|      0 |       |       |          |

-------------------------------------------------------------------------------------------------------------------------------------------------



Predicate Information (identified by operation id):

---------------------------------------------------



   4 - filter(("A"."ACCT_FLAG"='1' AND "A"."LAST_MODI_DATE"=TO_DATE(' 2013-12-31 00:00:00', 'syyyy-mm-dd hh24:mi:ss')))

   5 - access("A"."BUS_CODE"="B"."BUS_CODE")

   6 - filter((("A"."TERM"="B"."TERM" AND RTRIM("A"."SUB_CODE")=RTRIM("B"."SUB_CODE")) OR "A"."BUS_CODE"=77))





32 rows selected.





HASH JOIN:

Execution Plan

----------------------------------------------------------

Plan hash value: 4188551662



------------------------------------------------------------------------------------

| Id  | Operation           | Name         | Rows  | Bytes | Cost (%CPU)| Time     |

------------------------------------------------------------------------------------

|   0 | SELECT STATEMENT    |              |  8117 |   539K|  7768   (3)| 00:01:34 |

|   1 |  HASH GROUP BY      |              |  8117 |   539K|  7768   (3)| 00:01:34 |

|*  2 |   HASH JOIN         |              |  8117 |   539K|  7767   (3)| 00:01:34 |

|   3 |    TABLE ACCESS FULL| SAVC_BUSCODE |   409 | 10634 |     5   (0)| 00:00:01 |

|*  4 |    TABLE ACCESS FULL| COMR_INTDIST |  1136K|    45M|  7704   (2)| 00:01:33 |

------------------------------------------------------------------------------------



Predicate Information (identified by operation id):

---------------------------------------------------



   2 - access("A"."BUS_CODE"="B"."BUS_CODE")

       filter("A"."TERM"="B"."TERM" AND

              RTRIM("A"."SUB_CODE")=RTRIM("B"."SUB_CODE") OR "A"."BUS_CODE"=77)

   4 - filter("A"."ACCT_FLAG"='1' AND "A"."LAST_MODI_DATE"=TO_DATE('

              2013-12-31 00:00:00', 'syyyy-mm-dd hh24:mi:ss'))





Statistics

----------------------------------------------------------

          1  recursive calls

          2  db block gets

      27016  consistent gets

      26880  physical reads

          0  redo size

      37887  bytes sent via SQL*Net to client

       1147  bytes received via SQL*Net from client

         59  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

        860  rows processed



Plan hash value: 4188551662



----------------------------------------------------------------------------------------------------------------------------------

| Id  | Operation           | Name         | Starts | E-Rows | A-Rows |   A-Time   | Buffers | Reads  |  OMem |  1Mem | Used-Mem |

----------------------------------------------------------------------------------------------------------------------------------

|   0 | SELECT STATEMENT    |              |      1 |        |    860 |00:00:05.11 |   27018 |  26880 |       |       |          |

|   1 |  HASH GROUP BY      |              |      1 |   8117 |    860 |00:00:05.11 |   27018 |  26880 |   835K|   835K| 1456K (0)|

|*  2 |   HASH JOIN         |              |      1 |   8117 |   1131K|00:00:04.26 |   27018 |  26880 |   947K|   947K| 1257K (0)|

|   3 |    TABLE ACCESS FULL| SAVC_BUSCODE |      1 |    409 |    409 |00:00:00.01 |      21 |      0 |       |       |          |

|*  4 |    TABLE ACCESS FULL| COMR_INTDIST |      1 |   1136K|   1138K|00:00:00.69 |   26997 |  26880 |       |       |          |

----------------------------------------------------------------------------------------------------------------------------------



Predicate Information (identified by operation id):

---------------------------------------------------



   2 - access("A"."BUS_CODE"="B"."BUS_CODE")

       filter((("A"."TERM"="B"."TERM" AND RTRIM("A"."SUB_CODE")=RTRIM("B"."SUB_CODE")) OR "A"."BUS_CODE"=77))

   4 - filter(("A"."ACCT_FLAG"='1' AND "A"."LAST_MODI_DATE"=TO_DATE(' 2013-12-31 00:00:00', 'syyyy-mm-dd hh24:mi:ss')))





30 rows selected.