-----------------
| Id | Operation | Name | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | 3 (100)| |
| 1 | NESTED LOOPS | | 63 | 3 (0)| 00:00:01 |
| 2 | TABLE ACCESS BY INDEX ROWID| EMP | 33 | 2 (0)| 00:00:01 |
| 3 | INDEX UNIQUE SCAN | PK_EMP | | 1 (0)| 00:00:01 |
| 4 | TABLE ACCESS BY INDEX ROWID| DEPT | 12270 | 1 (0)| 00:00:01 |
| 5 | INDEX UNIQUE SCAN | PK_DEPT | | 0 (0)| |
--------------------------------------------------------------------------------
3、查看真实执行计划并获得统计信息
前提条件
设置参数statistics_level为all,可以基于session级别以及实例级别
或者启用gather_plan_statistics提示
/*-------------查看实例参数statistics_level的值，并在会话级别将其设定为all ---------*/
SQL> show parameter statistics_le
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
statistics_level string ALL
SQL> alter session set statistics_level=all;
Session altered.
SQL> select e.ename,e.sal,s.grade
2 from emp e
3 join salgrade s
4 on e.sal between losal and hisal
5 and e.deptno = 20 |