在10g以后我们可以通过利用gather_plan_statistics提示来了解更多的SQL执行统计信息，具体使用方法如下：
SQL> set linesize 150
SQL> set pagesize 2000
SQL> set autotrace traceonly exp
SQL> select avg(SALARY),DEPARTMENT_NAME from
employees e,departments d where e.DEPARTMENT_ID=d.DEPARTMENT_ID group by DEPARTMENT_NAME;
Execution Plan
----------------------------------------------------------
Plan hash value: 3294250112
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 27 | 621 | 5 (20)| 00:00:01 |
| 1 | HASH GROUP BY | | 27 | 621 | 5 (20)| 00:00:01 |
| 2 | NESTED LOOPS | | 106 | 2438 | 4 (0)| 00:00:01 |
| 3 | TABLE ACCESS FULL | EMPLOYEES | 107 | 749 | 3 (0)| 00:00:01 |
| 4 | TABLE ACCESS BY INDEX ROWID| DEPARTMENTS | 1 | 16 | 1 (0)| 00:00:01 |
|* 5 | INDEX UNIQUE SCAN | DEPT_ID_PK | 1 | | 0 (0)| 00:00:01 |
---------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
5 - access("E"."DEPARTMENT_ID"="D"."DEPARTMENT_ID")
SQL> show parameter cursor_sharing
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
cursor_sharing string EXACT
SQL> show parameter statistics_level
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
statistics_level string TYPICAL
SQL> set autotrace off;
SQL> select /*+ gather_plan_statistics */ avg(SALARY),DEPARTMENT_NAME from
employees e,departments d where e.DEPARTMENT_ID=d.DEPARTMENT_ID group by DEPARTMENT_NAME;
SQL> select * from TABLE(dbms_xplan.display_cursor(NULL,NULL,'ALLSTATS LAST'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID bctzu9xuxay18, child number 0
-------------------------------------
select /*+ gather_plan_statistics */ avg(SALARY),DEPARTMENT_NAME from employees e,departments d
where e.DEPARTMENT_ID=d.DEPARTMENT_ID group by DEPARTMENT_NAME
Plan hash value: 3294250112
-------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
-------------------------------------------------------------------------------------------------------
| 1 | HASH GROUP BY | | 1 | 27 | 11 |00:00:00.01 | 219 |
| 2 | NESTED LOOPS | | 1 | 106 | 106 |00:00:00.01 | 219 |
| 3 | TABLE ACCESS FULL | EMPLOYEES | 1 | 107 | 107 |00:00:00.01 | 7 |
| 4 | TABLE ACCESS BY INDEX ROWID| DEPARTMENTS | 107 | 1 | 106 |00:00:00.01 | 212 |
|* 5 | INDEX UNIQUE SCAN | DEPT_ID_PK | 107 | 1 | 106 |00:00:00.01 | 106 |
-------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
5 - access("E"."DEPARTMENT_ID"="D"."DEPARTMENT_ID")
/* 可以从starts列看到某种操作执行了多少次，例如这里的INDEX UNIQUE SCAN为107次 */
/*也可以通过SQL_ID来定位计划信息 */
SQL> select t.*
from v$sql s
, table(dbms_xplan.display_cursor(s.sql_id,s.child_number,'ALL IOSTATS LAST')) t where s.sql_id = '&SQL_ID' ;
Enter value for sql_id: bctzu9xuxay18
old 3: , table(dbms_xplan.display_cursor(s.sql_id,s.child_number,'ALL IOSTATS LAST')) t where s.sql_id = '&SQL_ID'
new 3: , table(dbms_xplan.display_cursor(s.sql_id,s.child_number,'ALL IOSTATS LAST')) t where s.sql_id = 'bctzu9xuxay18'
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID bctzu9xuxay18, child number 0
-------------------------------------
select /*+ gather_plan_statistics */ avg(SALARY),DEPARTMENT_NAME from
employees e,departments d where
e.DEPARTMENT_ID=d.DEPARTMENT_ID group by DEPARTMENT_NAME
Plan hash value: 3294250112
---------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers |
---------------------------------------------------------------------------------------------------------------------------------------
| 1 | HASH GROUP BY | | 1 | 27 | 621 | 5 (20)| 00:00:01 | 11 |00:00:00.01 | 219 |
| 2 | NESTED LOOPS | | 1 | 106 | 2438 | 4 (0)| 00:00:01 | 106 |00:00:00.01 | 219 |
| 3 | TABLE ACCESS FULL | EMPLOYEES | 1 | 107 | 749 | 3 (0)| 00:00:01 | 107 |00:00:00.01 | 7 |
| 4 | TABLE ACCESS BY INDEX ROWID| DEPARTMENTS | 107 | 1 | 16 | 1 (0)| 00:00:01 | 106 |00:00:00.01 | 212 |
|* 5 | INDEX UNIQUE SCAN | DEPT_ID_PK | 107 | 1 | | 0 (0)| | 106 |00:00:00.01 | 106 |
---------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1
3 - SEL$1 / E@SEL$1
4 - SEL$1 / D@SEL$1
5 - SEL$1 / D@SEL$1
Predicate Information (identified by operation id):
---------------------------------------------------
5 - access("E"."DEPARTMENT_ID"="D"."DEPARTMENT_ID")
Column Projection Information (identified by operation id):
-----------------------------------------------------------
1 - "DEPARTMENT_NAME"[VARCHAR2,30], AVG("SALARY")[22]
2 - "SALARY"[NUMBER,22], "DEPARTMENT_NAME"[VARCHAR2,30]
3 - "SALARY"[NUMBER,22], "E"."DEPARTMENT_ID"[NUMBER,22]
4 - "DEPARTMENT_NAME"[VARCHAR2,30]
5 - "D".ROWID[ROWID,10]
SQL> alter session set statistics_level=ALL;
Session altered.
/* 在session级别设置statistics_level为ALL,可以为我们提供更为详尽的执行统计信息 */
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