如何获取执行计划

如何oracle的获取执行计划
1.获取普通执行计划，效果类似于先执行set autot on exp;然后执行sql。
 explan plan for your_sql;
 select * from table(dbms_xplan.display);
2.获取具有outline信息的执行计划，用sqlprofile调优时非常有用，或者用这个执行计划了解更多oracle内部的hint
 explan plan for your_sql;
 select * from table(dbms_xplan.display(null, null,'advanced -projection'))
3.真实的执行计划，可以看到实际的 Starts（执行次数） | E-Rows（估算的返回行数） | A-Rows（实际的返回行数）
 ALTER SESSION SET STATISTICS_LEVEL=ALL; 
 execute your_sql;
 SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'ALLSTATS LAST'))
 
那么这3中获取执行计划的方式可以写到一个脚本getplan.sql，用的时候非常方便。
--getplan.sql
set feedback off timing off ver off
pro 'general,outline,starts'
pro
acc type prompt 'Enter value for plan type:' default 'general'
SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'ALLSTATS LAST')) where '&&type'='starts';
select * from table(dbms_xplan.display) where '&&type'='general';
select * from table(dbms_xplan.display(null, null,'advanced -projection')) where '&&type'='outline';
set feedback on timing on ver on
undef type


测试如下：
SQL> select * from a;

 ID NAME
---------- ----------
 1 a1
 2 a2
 3 a3
 4 a4
 5 a5
SQL> select * from b;

 ID NAME
---------- ----------
 1 b1
 2 b2
 
 
 
--执行计划1：普通执行计划
SQL> explain plan for select a.*,(select name from b where b.id=a.id) from a;

Explained.

Elapsed: 00:00:00.04
SQL> @getplan
'general,outline,starts'

Enter value for plan type: ----这里输入general或回车

PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------
Plan hash value: 3653839899

--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 5 | 100 | 3 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| B | 1 | 20 | 3 (0)| 00:00:01 |
| 2 | TABLE ACCESS FULL| A | 5 | 100 | 3 (0)| 00:00:01 |
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

 1 - filter("B"."ID"=:B1)

Note
-----
 - dynamic sampling used for this statement
 
 
 
--执行计划2：outline执行计划
SQL> explain plan for select a.*,(select name from b where b.id=a.id) from a;

Explained.

Elapsed: 00:00:00.01
SQL> @getplan
'general,outline,starts'

Enter value for plan type:outline --这里输入outline

PLAN_TABLE_OUTPUT
---------------------------------------------------------------------------------------
Plan hash value: 3653839899

--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 5 | 100 | 3 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| B | 1 | 20 | 3 (0)| 00:00:01 |
| 2 | TABLE ACCESS FULL| A | 5 | 100 | 3 (0)| 00:00:01 |
--------------------------------------------------------------------------

Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------

 1 - SEL$2 / B@SEL$2
 2 - SEL$1 / A@SEL$1

Outline Data
-------------

 /*+
 BEGIN_OUTLINE_DATA
 FULL(@"SEL$2" "B"@"SEL$2")
 FULL(@"SEL$1" "A"@"SEL$1")
 OUTLINE_LEAF(@"SEL$1")
 OUTLINE_LEAF(@"SEL$2")
 ALL_ROWS
 OPTIMIZER_FEATURES_ENABLE('10.2.0.4')
 IGNORE_OPTIM_EMBEDDED_HINTS
 END_OUTLINE_DATA
 */

Predicate Information (identified by operation id):
---------------------------------------------------

 1 - filter("B"."ID"=:B1)

Note
-----
 - dynamic sampling used for this statement 




--执行计划3：real执行计划
SQL> set serveroutput off
SQL> ALTER SESSION SET STATISTICS_LEVEL=ALL;

Session altered.

Elapsed: 00:00:00.00
SQL> select a.*,(select name from b where b.id=a.id) from a;

 ID NAME (SELECTNAM
---------- ---------- ----------
 1 a1 b1
 2 a2 b2
 3 a3
 4 a4
 5 a5

5 rows selected.

Elapsed: 00:00:00.03
SQL> @getplan
'general,outline,starts'

Enter value for plan type:starts --这里输入starts

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------
SQL_ID 8rv825dykpx1m, child number 0
-------------------------------------
select a.*,(select name from b where b.id=a.id) from a

Plan hash value: 3653839899

------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
------------------------------------------------------------------------------------
|* 1 | TABLE ACCESS FULL| B | 5 | 1 | 2 |00:00:00.01 | 35 |
| 2 | TABLE ACCESS FULL| A | 1 | 5 | 5 |00:00:00.01 | 8 |
------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

 1 - filter("B"."ID"=:B1)

Note
-----
 - dynamic sampling used for this statement

--注意：
--第3种执行计划不能多次获取，只能执行1次，获取一次，否则会获取不到
下面再次获取一下试试：
SQL> @getplan
'general,outline,starts'

Enter value for plan type:starts

PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------
SQL_ID dvp8nn63wuhs8, child number 0
-------------------------------------
select * from table(dbms_xplan.display(null, null,'advanced -projection'))
where 'starts'='outline'

Plan hash value: 3440229843

-------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | A-Rows | A-Time |
-------------------------------------------------------------------------------------
|* 1 | FILTER | | 1 | 0 |00:00:00.01 |
| 2 | COLLECTION ITERATOR PICKLER FETCH| DISPLAY | 0 | 0 |00:00:00.01 | --第二次无法获取真实的执行计划
-------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

 1 - filter(NULL IS NOT NULL)

Note
-----
 - rule based optimizer used (consider using cbo)
 
 
--第3种执行计划要关掉set serveroutput off，否则也不能获取执行计划。
测试如下：
这里和上面的测试是同一个会话，所以没有再执行ALTER SESSION SET STATISTICS_LEVEL=ALL;了。
SQL> set serveroutput on
SQL> select a.*,(select name from b where b.id=a.id) from a;

 ID NAME (SELECTNAM
---------- ---------- ----------
 1 a1 b1
 2 a2 b2
 3 a3
 4 a4
 5 a5

5 rows selected.

Elapsed: 00:00:00.03
SQL> @getplan
'general,outline,starts'

Enter value for plan type:starts

PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------------------------------
SQL_ID 9babjv8yq8ru3, child number 0

BEGIN DBMS_OUTPUT.GET_LINES(:LINES, :NUMLINES); END; --也无法获取真实的执行计划

NOTE: cannot fetch plan for SQL_ID: 9babjv8yq8ru3, CHILD_NUMBER: 0
 Please verify value of SQL_ID and CHILD_NUMBER;
 It could also be that the plan is no longer in cursor cache (check v$sql_plan)