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.