如何能在執行計劃中看到Starts

eric0435發表於2013-06-29
SQL> explain plan for
  2
  2  SELECT *
  3  FROM scott.emp
  4  WHERE NOT EXISTS (SELECT 0
  5  FROM scott.dept
  6  WHERE dept.dname = 'SALES' AND dept.deptno = emp.deptno)
  7  AND NOT EXISTS (SELECT 0
  8  FROM scott.bonus
  9  WHERE bonus.ename = emp.ename);

Explained

SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 734347697
-----------------------------------------------------------------------------
| Id  | Operation           | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |       |     9 |   522 |     9  (12)| 00:00:01 |
|*  1 |  HASH JOIN ANTI     |       |     9 |   522 |     9  (12)| 00:00:01 |
|*  2 |   HASH JOIN ANTI    |       |     9 |   459 |     7  (15)| 00:00:01 |
|   3 |    TABLE ACCESS FULL| EMP   |    14 |   532 |     3   (0)| 00:00:01 |
|*  4 |    TABLE ACCESS FULL| DEPT  |     1 |    13 |     3   (0)| 00:00:01 |
|   5 |   TABLE ACCESS FULL | BONUS |     1 |     7 |     2   (0)| 00:00:01 |
-----------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - access("BONUS"."ENAME"="EMP"."ENAME")
   2 - access("DEPT"."DEPTNO"="EMP"."DEPTNO")
   4 - filter("DEPT"."DNAME"='SALES')

使用advanced也不顯示
SQL> explain plan for select * from scott.emp;

Explained

SQL> SELECT * FROM table(dbms_xplan.display(NULL,NULL,'advanced'));

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 3956160932
--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |    14 |   532 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| EMP  |    14 |   532 |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
   1 - SEL$1 / EMP@SEL$1
Outline Data
-------------
  /*+
      BEGIN_OUTLINE_DATA
      FULL(@"SEL$1" "EMP"@"SEL$1")

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
      OUTLINE_LEAF(@"SEL$1")
      ALL_ROWS
      DB_VERSION('11.2.0.1')
      OPTIMIZER_FEATURES_ENABLE('11.2.0.1')
      IGNORE_OPTIM_EMBEDDED_HINTS
      END_OUTLINE_DATA
  */
Column Projection Information (identified by operation id):
-----------------------------------------------------------
   1 - "EMP"."EMPNO"[NUMBER,22], "EMP"."ENAME"[VARCHAR2,10],
       "EMP"."JOB"[VARCHAR2,9], "EMP"."MGR"[NUMBER,22],
       "EMP"."HIREDATE"[DATE,7], "EMP"."SAL"[NUMBER,22],
       "EMP"."COMM"[NUMBER,22], "EMP"."DEPTNO"[NUMBER,22]


要得到starts要麼在SQLPLUS中將statistics_level設定all，並真實執行sql語句
因為display_cursor是從動態效能檢視v$session,v$sql,v$sql_plan和v$sql_plan_statistics_all中獲取直接計劃的使用explain plan for不行
因為它只生成執行計劃並沒真正地執行而且執行計劃是儲存在plan_table表中
並使用display來顯示

要麼在要執行的sql語句中statistics_level 仍然保留'typical' ，
然後用這個HINT/*+gather_plan_statistics */
SQL> alter session set statistics_level=all;

會話已更改。

SQL> select count(*) from scott.emp;

  COUNT(*)
----------
        14


SQL> select * from table(dbms_xplan.display_cursor(null,null,'allstats'));

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

SQL_ID  abj9tmfcs15bm, child number 0
-------------------------------------
select count(*) from scott.emp

Plan hash value: 2937609675

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

| Id  | Operation        | Name   | Starts | E-Rows | A-Rows |   A-Time   | Buffers |

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

|   0 | SELECT STATEMENT |        |      1 |        |      1 |00:00:00.01 |  1 |

|   1 |  SORT AGGREGATE  |        |      1 |      1 |      1 |00:00:00.01 |  1 |

|   2 |   INDEX FULL SCAN| PK_EMP |      1 |     14 |     14 |00:00:00.01 |  1 |

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



已選擇14行。

SQL>



SQL> alter session set statistics_level='typical';

會話已更改。


SQL> select /*+gather_plan_statistics */ count(*) from scott.emp;

  COUNT(*)
----------
        14

SQL> select * from table(dbms_xplan.display_cursor(null,null,'allstats'));

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

SQL_ID  2vku9s3sb55tz, child number 0
-------------------------------------
select /*+gather_plan_statistics */ count(*) from scott.emp

Plan hash value: 2937609675

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

| Id  | Operation        | Name   | Starts | E-Rows | A-Rows |   A-Time   | Buffers |

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------


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

|   0 | SELECT STATEMENT |        |      1 |        |      1 |00:00:00.01 |  1 |

|   1 |  SORT AGGREGATE  |        |      1 |      1 |      1 |00:00:00.01 |  1 |

|   2 |   INDEX FULL SCAN| PK_EMP |      1 |     14 |     14 |00:00:00.01 |  1 |

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



已選擇14行。

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