-- 这里是SQL语句 select empno,ename from emp 的执行计划-- 第一部分

SQL_ID  78bd3uh4a08av, child number 0
-------------------------------------
select empno,ename from empPlan hash value: 3956160932-- 第二部分 （主体部分）
-- 这里主要关注部分，可以看到执行时的执行步骤，执行顺序，对应的谓词信息、列信息， 消耗成本等
-------------------------------------------
| Id  | Operation         | Name | E-Rows |
-------------------------------------------
|   0 | SELECT STATEMENT  |      |        |
|   1 |  TABLE ACCESS FULL| EMP  |     16 |
--------------------------------------------- 第三部分 （补充说明）
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

-- 1.执行 explain 命令SQL，这里的for后面为需要查看执行计划的SQL语句：
explain plan for select * from emp;-- 2.执行如下语句 select * from table(dbms_xplan.display）-- 得到执行结果如下：
Plan hash value: 3956160932--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |    16 |   592 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| EMP  |    16 |   592 |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------

-- 这里的all和advanced都行，二选一。但是必须是从dos窗口中执行，它会取上一次执行的SQL的执行计划返回。
select * from table(dbms_xplan.display_cursor(null,null,'all/advanced'));-- 通过使用该SQL查询执行过的SQL语句的SQLid
SELECT SQL_ID FROM v$SQL  WHERE SQL_TEXT like'select * from emp'
-- 查询该SQL的执行计划，需要在同一个session中执行。
select * from table(dbms_xplan.display_cursor('sql_id/hash_value',child_cursor_number,'all/advanced'));

SQL_ID  a2dk8bdn0ujx7, child number 0
-------------------------------------
select * from empPlan hash value: 3956160932--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |       |       |     3 (100)|          |
|   1 |  TABLE ACCESS FULL| EMP  |    16 |   592 |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------

Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------1 - SEL$1 / EMP@SEL$1Column 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]

SQL_ID  22svdfk7watap, child number 0
-------------------------------------
select emp.ename,EMP_TEMP.EMPNO from emp,EMP_TEMP where emp.ename in
(select ename from EMP_TEMP where empno > 100)Plan hash value: 1993712166----------------------------------------------------------------------------------
| Id  | Operation             | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |          |       |       |    16 (100)|          |
|*  1 |  HASH JOIN            |          |   194 |  4074 |    16   (7)| 00:00:01 |
|   2 |   MERGE JOIN CARTESIAN|          |   182 |  2730 |    13   (8)| 00:00:01 |
|   3 |    SORT UNIQUE        |          |    14 |   154 |     3   (0)| 00:00:01 |
|*  4 |     TABLE ACCESS FULL | EMP_TEMP |    14 |   154 |     3   (0)| 00:00:01 |
|   5 |    BUFFER SORT        |          |    14 |    56 |    10  (10)| 00:00:01 |
|   6 |     TABLE ACCESS FULL | EMP_TEMP |    14 |    56 |     1   (0)| 00:00:01 |
|   7 |   TABLE ACCESS FULL   | EMP      |    16 |    96 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------------

Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------1 - SEL$5DA710D34 - SEL$5DA710D3 / EMP_TEMP@SEL$26 - SEL$5DA710D3 / EMP_TEMP@SEL$17 - SEL$5DA710D3 / EMP@SEL$1Predicate Information (identified by operation id):
---------------------------------------------------1 - access("EMP"."ENAME"="ENAME")4 - filter("EMPNO">100)Column Projection Information (identified by operation id):
-----------------------------------------------------------1 - (#keys=1) "EMP"."ENAME"[VARCHAR2,10], "EMP_TEMP"."EMPNO"[NUMBER,22]2 - "ENAME"[VARCHAR2,10], "EMP_TEMP"."EMPNO"[NUMBER,22]3 - (#keys=1) "ENAME"[VARCHAR2,10]4 - (rowset=256) "ENAME"[VARCHAR2,10]5 - (#keys=0) "EMP_TEMP"."EMPNO"[NUMBER,22]6 - (rowset=256) "EMP_TEMP"."EMPNO"[NUMBER,22]7 - (rowset=256) "EMP"."ENAME"[VARCHAR2,10]