oracle 执行计划修改学习---query block

*************************************************************
t1表有100行记录
t2表有1M行记录
t1表T1"."N" 有索引
t2表T2"."T1_ID"有索引

=------正确执行计划应该为：

SQL_ID  cgwuncwm2pryk, child number 0
-------------------------------------
SELECT * FROM t1, t2 WHERE t1.id = t2.t1_id AND t1.n <= 19

Plan hash value: 2669480776

-------------------------------------------------------------------------------------------------------------
| Id  | Operation                     | Name     | Starts | E-Rows | A-Rows |   A-Time   | Buffers | Reads  |
-------------------------------------------------------------------------------------------------------------
|   1 |  TABLE ACCESS BY INDEX ROWID  | T2       |      1 |      1 |     19 |00:00:00.01 |      49 |      3 |
|   2 |   NESTED LOOPS                |          |      1 |     24 |     39 |00:00:00.01 |      30 |      0 |
|   3 |    TABLE ACCESS BY INDEX ROWID| T1       |      1 |     24 |     19 |00:00:00.01 |       6 |      0 |
|*  4 |     INDEX RANGE SCAN          | T1_N     |      1 |     24 |     19 |00:00:00.01 |       3 |      0 |
|*  5 |    INDEX RANGE SCAN           | T2_T1_ID |     19 |      1 |     19 |00:00:00.01 |      24 |      0 |
-------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   4 - access("T1"."N"<=19)
   5 - access("T1"."ID"="T2"."T1_ID")
22 rows selected.


----手工设置表的统计信息，使oracle cbo 误认为t2为小表，t1 为大表
EXEC  dbms_stats.SET_table_stats(user, 'T1', numrows => 200000000  ,numblks => 1000000);
EXEC  dbms_stats.SET_table_stats(user, 'T2', numrows => 1  ,numblks => 1);



*************************************************************
----这里只添加一行使用T2"."T1_ID 的索引的大纲hint


SQL_ID  gjdju6xucw779, child number 0
-------------------------------------
SELECT /*+ INDEX(@"SEL$1" "T2"@"SEL$1" ("T2"."T1_ID")) */ * FROM t1, t2 WHERE t1.id
=t2.t1_id AND t1.n <= 19


Plan hash value: 2481503312
----------------------------------------------------------------------------------------------------
| Id  | Operation                     | Name     | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
----------------------------------------------------------------------------------------------------
|*  1 |  TABLE ACCESS BY INDEX ROWID  | T1       |      1 |     49 |     19 |00:00:57.44 |     100K|
|   2 |   NESTED LOOPS                |          |      1 |     49 |   2000K|00:00:39.16 |     100K|
|   3 |    TABLE ACCESS BY INDEX ROWID| T2       |      1 |      1 |    100K|00:00:02.70 |     100K|
|   4 |     INDEX FULL SCAN           | T2_T1_ID |      1 |      1 |    100K|00:00:00.66 |     225 |
|*  5 |    INDEX RANGE SCAN           | T1_N     |    100K|    100 |   1900K|00:00:13.51 |       5 |
----------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
   1 - SEL$1 / T1@SEL$1
   3 - SEL$1 / T2@SEL$1
   4 - SEL$1 / T2@SEL$1
   5 - SEL$1 / T1@SEL$1

Outline Data
-------------
  /*+
      BEGIN_OUTLINE_DATA
      IGNORE_OPTIM_EMBEDDED_HINTS
      OPTIMIZER_FEATURES_ENABLE('10.2.0.1')
      ALL_ROWS
      OUTLINE_LEAF(@"SEL$1")
      INDEX(@"SEL$1" "T2"@"SEL$1" ("T2"."T1_ID"))
      INDEX(@"SEL$1" "T1"@"SEL$1" ("T1"."N"))
      LEADING(@"SEL$1" "T2"@"SEL$1" "T1"@"SEL$1")
      USE_NL(@"SEL$1" "T1"@"SEL$1")
      END_OUTLINE_DATA
  */


Predicate Information (identified by operation id):
--------------------------------------------------
   1 - filter("T1"."ID"="T2"."T1_ID")
   5 - access("T1"."N"<=19)


47 rows selected.
SQL> 

***********************************************
***********************************************
----通过修改大纲hint信息来影响执行计划，这里添加了t2 表的索引hint， t1作为驱动表的hint，使用nl 的hint


SELECT 
/*+ 
INDEX(@"SEL$1" "T2"@"SEL$1" ("T2"."T1_ID"))  
LEADING(@"SEL$1" "T1"@"SEL$1" "T2"@"SEL$1") 
USE_NL(@"SEL$1" "T2"@"SEL$1") 
*/ * 

FROM t1, t2 WHERE t1.id=t2.t1_id AND t1.n <= 19；

SQL_ID  0106c7pwnv5hh, child number 0
-------------------------------------
SELECT /*+ INDEX(@"SEL$1" "T2"@"SEL$1" ("T2"."T1_ID"))  LEADING(@"SEL$1" "T1"@"SEL$1"
"T2"@"SEL$1") USE_NL(@"SEL$1" "T2"@"SEL$1") */ * FROM t1, t2 WHERE t1.id=t2.t1_id AND t1.n
<= 19


Plan hash value: 2669480776


----------------------------------------------------------------------------------------------------
| Id  | Operation                     | Name     | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
----------------------------------------------------------------------------------------------------
|   1 |  TABLE ACCESS BY INDEX ROWID  | T2       |      1 |      1 |     19 |00:00:00.01 |      49 |
|   2 |   NESTED LOOPS                |          |      1 |     49 |     39 |00:00:00.01 |      30 |
|   3 |    TABLE ACCESS BY INDEX ROWID| T1       |      1 |   4800K|     19 |00:00:00.01 |       6 |
|*  4 |     INDEX RANGE SCAN          | T1_N     |      1 |    100 |     19 |00:00:00.01 |       3 |
|*  5 |    INDEX RANGE SCAN           | T2_T1_ID |     19 |      1 |     19 |00:00:00.01 |      24 |
----------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
   1 - SEL$1 / T2@SEL$1
   3 - SEL$1 / T1@SEL$1
   4 - SEL$1 / T1@SEL$1
   5 - SEL$1 / T2@SEL$1
Outline Data
-------------
  /*+
      BEGIN_OUTLINE_DATA
      IGNORE_OPTIM_EMBEDDED_HINTS
      OPTIMIZER_FEATURES_ENABLE('10.2.0.1')
      ALL_ROWS
      OUTLINE_LEAF(@"SEL$1")
      INDEX(@"SEL$1" "T1"@"SEL$1" ("T1"."N"))
      INDEX(@"SEL$1" "T2"@"SEL$1" ("T2"."T1_ID"))
      LEADING(@"SEL$1" "T1"@"SEL$1" "T2"@"SEL$1")
      USE_NL(@"SEL$1" "T2"@"SEL$1")
      END_OUTLINE_DATA
  */


Predicate Information (identified by operation id):
---------------------------------------------------
   4 - access("T1"."N"<=19)
   5 - access("T1"."ID"="T2"."T1_ID")
48 rows selected.



*************************************************************
-----只是用nl 小表驱动hint：

SQL_ID  bannu3t7caycc, child number 0
-------------------------------------
SELECT /*+ leading(t1) use_nl(t2) */ * FROM t1, t2 WHERE t1.id = t2.t1_id AND t1.n <= 19


Plan hash value: 76617097


--------------------------------------------------------------------------------------------------------
| Id  | Operation                    | Name | Starts | E-Rows | A-Rows |   A-Time   | Buffers | Reads  |
--------------------------------------------------------------------------------------------------------
|   1 |  NESTED LOOPS                |      |      1 |     49 |     19 |00:00:00.07 |   18723 |    983 |
|   2 |   TABLE ACCESS BY INDEX ROWID| T1   |      1 |   4800K|     19 |00:00:00.01 |       6 |      2 |
|*  3 |    INDEX RANGE SCAN          | T1_N |      1 |    100 |     19 |00:00:00.01 |       3 |      1 |
|*  4 |   TABLE ACCESS FULL          | T2   |     19 |      1 |     19 |00:00:00.07 |   18717 |    981 |
--------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------


   1 - SEL$1
   2 - SEL$1 / T1@SEL$1
   3 - SEL$1 / T1@SEL$1
   4 - SEL$1 / T2@SEL$1


Outline Data
-------------
  /*+
      BEGIN_OUTLINE_DATA
      IGNORE_OPTIM_EMBEDDED_HINTS
      OPTIMIZER_FEATURES_ENABLE('10.2.0.1')
      ALL_ROWS
      OUTLINE_LEAF(@"SEL$1")
      INDEX(@"SEL$1" "T1"@"SEL$1" ("T1"."N"))
      FULL(@"SEL$1" "T2"@"SEL$1")
      LEADING(@"SEL$1" "T1"@"SEL$1" "T2"@"SEL$1")
      USE_NL(@"SEL$1" "T2"@"SEL$1")
      END_OUTLINE_DATA
  */


Predicate Information (identified by operation id):
---------------------------------------------------
   3 - access("T1"."N"<=19)
   4 - filter("T1"."ID"="T2"."T1_ID")
45 rows selected.


！！！！！但是("T2"."T1_ID") 表上的索引 T2_T1_ID 还是用没有被oracle的optimize 优化器采用（为什么没有自动使用没有想明白？）

*******************************************************
----添加索引 nl 的hint：
SQL_ID  300a951pfx6vn, child number 0
-------------------------------------
SELECT /*+ leading(t1) use_nl(t2) index(t2 T2_T1_ID) */ * FROM t1, t2 WHERE t1.id = t2.t1_id AND
t1.n <= 19


Plan hash value: 266948077
-------------------------------------------------------------------------------------------------------------
| Id  | Operation                     | Name     | Starts | E-Rows | A-Rows |   A-Time   | Buffers | Reads  |
-------------------------------------------------------------------------------------------------------------
|   1 |  TABLE ACCESS BY INDEX ROWID  | T2       |      1 |      1 |     19 |00:00:00.01 |      49 |      2 |
|   2 |   NESTED LOOPS                |          |      1 |     49 |     39 |00:00:00.01 |      30 |      2 |
|   3 |    TABLE ACCESS BY INDEX ROWID| T1       |      1 |   4800K|     19 |00:00:00.01 |       6 |      0 |
|*  4 |     INDEX RANGE SCAN          | T1_N     |      1 |    100 |     19 |00:00:00.01 |       3 |      0 |
|*  5 |    INDEX RANGE SCAN           | T2_T1_ID |     19 |      1 |     19 |00:00:00.01 |      24 |      2 |
-------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
   1 - SEL$1 / T2@SEL$1
   3 - SEL$1 / T1@SEL$1
   4 - SEL$1 / T1@SEL$1
   5 - SEL$1 / T2@SEL$1


Outline Data
-------------
  /*+
      BEGIN_OUTLINE_DATA
      IGNORE_OPTIM_EMBEDDED_HINTS
      OPTIMIZER_FEATURES_ENABLE('10.2.0.1')
      ALL_ROWS
      OUTLINE_LEAF(@"SEL$1")
      INDEX(@"SEL$1" "T1"@"SEL$1" ("T1"."N"))
      INDEX(@"SEL$1" "T2"@"SEL$1" ("T2"."T1_ID"))
      LEADING(@"SEL$1" "T1"@"SEL$1" "T2"@"SEL$1")
      USE_NL(@"SEL$1" "T2"@"SEL$1")
      END_OUTLINE_DATA
  */


Predicate Information (identified by operation id):
---------------------------------------------------
   4 - access("T1"."N"<=19)
   5 - access("T1"."ID"="T2"."T1_ID")
47 rows selected.



---------关于大纲hint 的信息简化写法
INDEX  
语法：INDEX([<@查询块>] <表> [<索引>]) 或者 INDEX([<@查询块>] <表> [(<索引字段列表>)]) 
描述：指示优化器通过索引来访问和扫描表。

SQL_ID  2uc505kd7jsj8, child number 0
-------------------------------------
SELECT /*+  
INDEX(T2(T2.T1_ID))  ------索引的hint也可以这么写 
LEADING(T1 T2)  
USE_NL(T2) 
*/ * FROM t1, t2 WHERE t1.id=t2.t1_id AND t1.n <= 19

Plan hash value: 2669480776
----------------------------------------------------------------------------------------------------
| Id  | Operation                     | Name     | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
----------------------------------------------------------------------------------------------------
|   1 |  TABLE ACCESS BY INDEX ROWID  | T2       |      1 |      1 |     19 |00:00:00.01 |      49 |
|   2 |   NESTED LOOPS                |          |      1 |     49 |     39 |00:00:00.01 |      30 |
|   3 |    TABLE ACCESS BY INDEX ROWID| T1       |      1 |   4800K|     19 |00:00:00.01 |       6 |
|*  4 |     INDEX RANGE SCAN          | T1_N     |      1 |    100 |     19 |00:00:00.01 |       3 |
|*  5 |    INDEX RANGE SCAN           | T2_T1_ID |     19 |      1 |     19 |00:00:00.01 |      24 |
----------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
   1 - SEL$1 / T2@SEL$1
   3 - SEL$1 / T1@SEL$1
   4 - SEL$1 / T1@SEL$1
   5 - SEL$1 / T2@SEL$1
Outline Data
------------
  /*+
      BEGIN_OUTLINE_DATA
      IGNORE_OPTIM_EMBEDDED_HINTS
      OPTIMIZER_FEATURES_ENABLE('10.2.0.1')
      ALL_ROWS
      OUTLINE_LEAF(@"SEL$1")
      INDEX(@"SEL$1" "T1"@"SEL$1" ("T1"."N"))
      INDEX(@"SEL$1" "T2"@"SEL$1" ("T2"."T1_ID"))
      LEADING(@"SEL$1" "T1"@"SEL$1" "T2"@"SEL$1")
      USE_NL(@"SEL$1" "T2"@"SEL$1")
      END_OUTLINE_DATA
  */


Predicate Information (identified by operation id):
---------------------------------------------------
   4 - access("T1"."N"<=19)
   5 - access("T1"."ID"="T2"."T1_ID")

47 rows selected.

SQL> 

SQL_ID  2qz4v29ugrh94, child number 0
-------------------------------------
SELECT /*+  INDEX(T2)  LEADING(T1 T2)  USE_NL(T2) */ * FROM t1, t2 WHERE t1.id=t2.t1_id AND
t1.n <= 19
Plan hash value: 2669480776
----------------------------------------------------------------------------------------------------
| Id  | Operation                     | Name     | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
----------------------------------------------------------------------------------------------------
|   1 |  TABLE ACCESS BY INDEX ROWID  | T2       |      1 |      1 |     19 |00:00:00.01 |      49 |
|   2 |   NESTED LOOPS                |          |      1 |     49 |     39 |00:00:00.01 |      30 |
|   3 |    TABLE ACCESS BY INDEX ROWID| T1       |      1 |   4800K|     19 |00:00:00.01 |       6 |
|*  4 |     INDEX RANGE SCAN          | T1_N     |      1 |    100 |     19 |00:00:00.01 |       3 |
|*  5 |    INDEX RANGE SCAN           | T2_T1_ID |     19 |      1 |     19 |00:00:00.01 |      24 |
----------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
   1 - SEL$1 / T2@SEL$1
   3 - SEL$1 / T1@SEL$1
   4 - SEL$1 / T1@SEL$1
   5 - SEL$1 / T2@SEL$1

Outline Data
-------------
  /*+
      BEGIN_OUTLINE_DATA
      IGNORE_OPTIM_EMBEDDED_HINTS
      OPTIMIZER_FEATURES_ENABLE('10.2.0.1')
      ALL_ROWS
      OUTLINE_LEAF(@"SEL$1")
      INDEX(@"SEL$1" "T1"@"SEL$1" ("T1"."N"))
      INDEX(@"SEL$1" "T2"@"SEL$1" ("T2"."T1_ID"))
      LEADING(@"SEL$1" "T1"@"SEL$1" "T2"@"SEL$1")
      USE_NL(@"SEL$1" "T2"@"SEL$1")
      END_OUTLINE_DATA
  */

Predicate Information (identified by operation id):
---------------------------------------------------
   4 - access("T1"."N"<=19)
   5 - access("T1"."ID"="T2"."T1_ID")
47 rows selected.
SQL>