如何快速得到真实的执行计划

准备工作： create table zbdba as select * from dba_objects;create table zbdba1 as select * from dba_objects;create index zbdba_owner on zbdba(owner);create index zbdba1_owner on zbdba1(owner);exec dbms_stats.gather_table_stats(user, ZBDBA,

create table zbdba as select * from dba_objects;
create table zbdba1 as select * from dba_objects;
create index zbdba_owner on zbdba(owner);
create index zbdba1_owner on zbdba1(owner);
exec dbms_stats.gather_table_stats(user, 'ZBDBA', method_opt => 'FOR ALL COLUMNS SIZE 1');
exec dbms_stats.gather_table_stats(user, 'ZBDBA1', method_opt => 'FOR ALL COLUMNS SIZE 1');

explain plan for select zbdba.object_name from zbdba,zbdba1 where zbdba.owner=zbdba1.owner
SCOTT@orcl11g>select plan_table_output from table(dbms_xplan.display());
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 1287183320
----------------------------------------------------------------------------------------------
| Id  | Operation             | Name         | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |              |   207M|  7330M|       |  1198  (55)| 00:00:15 |
|*  1 |  HASH JOIN            |              |   207M|  7330M|  1272K|  1198  (55)| 00:00:15 |
|   2 |   INDEX FAST FULL SCAN| ZBDBA1_OWNER | 72068 |   422K|       |    48   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL   | ZBDBA        | 72067 |  2181K|       |   288   (1)| 00:00:04 |
----------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - access("ZBDBA"."OWNER"="ZBDBA1"."OWNER")
15 rows selected.

但是这种执行计划不一定是准确的。那我们怎么能才能快速的得到准确的执行计划呢？

真实的执行计划就是已经执行的sql

那么

select zbdba.object_name from zbdba,zbdba1 where zbdba.owner=zbdba1.owner;
你不需要一直等，ctrl+c中断即可
SCOTT@orcl11g>select sql_text,sql_id,hash_value,child_number from v$sql where sql_text like 'select zbdba.object_name from zbdba,zbdba1 where zbdba.owner=zbdba1.owner%';
SQL_TEXT                                                     SQL_ID                     HASH_VALUE CHILD_NUMBER
------------------------------------------------------------ -------------------------- ---------- ------------
select zbdba.object_name from zbdba,zbdba1 where zbdba.owner fr4g7ypwx5krq              2043857654            0
=zbdba1.owner
SCOTT@orcl11g>select * from table(dbms_xplan.display_cursor('fr4g7ypwx5krq',0,'ALLSTATS LAST'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------
SQL_ID  fr4g7ypwx5krq, child number 0
-------------------------------------
select zbdba.object_name from zbdba,zbdba1 where
zbdba.owner=zbdba1.owner
Plan hash value: 1287183320
----------------------------------------------------------------------------------
| Id  | Operation             | Name         | E-Rows |  OMem |  1Mem | Used-Mem |
----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |              |        |       |       |          |
|*  1 |  HASH JOIN            |              |    207M|  3024K|  1862K| 7066K (0)|
|   2 |   INDEX FAST FULL SCAN| ZBDBA1_OWNER |  72068 |       |       |          |
|   3 |   TABLE ACCESS FULL   | ZBDBA        |  72067 |       |       |          |
----------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - access("ZBDBA"."OWNER"="ZBDBA1"."OWNER")
Note
-----
   - Warning: basic plan statistics not available. These are only collected when:
       * hint 'gather_plan_statistics' is used for the statement or
       * parameter 'statistics_level' is set to 'ALL', at session or system level
27 rows selected.