SQL Tuning 基础概述02 - Explain plan的使用

1.explain plan的使用

SQL> explain plan for delete from t_jingyu;



Explained.



SQL> select * from table(dbms_xplan.display);



PLAN_TABLE_OUTPUT

--------------------------------------------------------------------------------------------------------------------------------------------

Plan hash value: 1368587462



-----------------------------------------------------------------------

| Id  | Operation          | Name     | Rows  | Cost (%CPU)| Time     |

-----------------------------------------------------------------------

|   0 | DELETE STATEMENT   |          |  1864K|   978   (2)| 00:00:12 |

|   1 |  DELETE            | T_JINGYU |       |            |          |

|   2 |   TABLE ACCESS FULL| T_JINGYU |  1864K|   978   (2)| 00:00:12 |

-----------------------------------------------------------------------



Note

-----

   - dynamic sampling used for this statement (level=2)



13 rows selected

 2.explain plan 只是显示执行计划，并不会真正执行delete语句·

SQL> select count(*) from t_jingyu;



  COUNT(*)

----------

   2097152