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.
