oracle如何产生sql 执行计划（二）

oracle如何产生sql 执行计划（二）

    今天是2013-09-23，之前写过一篇笔记是《oracle如何产生sql执行计划（一）》，那么除了这一种方法以外其实还有两种（据我所知）。
今天就看看另外另种：
一、explain plan sql
该语句可以对sql直接执行计划，执行的计划存储在表plan_table这张表中，但这太繁琐了，每个表的字段需要自己定义。
我习惯使用dbms_xplan这个软件包，
看一下这个包的介绍：
The

DBMS_XPLAN

package provides an easy way to display the output of the

EXPLAIN

PLAN

command in several, predefined formats. You can also use the

DBMS_XPLAN

package to display the plan of a statement stored in the Automatic Workload Repository (AWR) or stored in a SQL tuning set. It further provides a way to display
the SQL execution plan and SQL execution runtime statistics for cached SQL cursors based on the information stored in the

V$SQL_PLAN

and

V$SQL_PLAN_STATISTICS_ALL

fixed views. Finally, it displays plans from a SQL plan baseline.
然后看一下这个包的函数有哪些：

DISPLAY

- to format and display the contents of a plan table.

DISPLAY_AWR

- to format and display the contents of the execution plan of a stored SQL statement in the AWR.

DISPLAY_CURSOR

- to format and display the contents of the execution plan of any loaded cursor.

DISPLAY_SQL_PLAN_BASELINE

- to display one or more execution plans for the SQL statement identified by SQL handle

DISPLAY_SQLSET

- to format and display the contents of the execution plan of statements stored in a SQL tuning set.

 

我常用的两个如下。
1）displan ：格式化然后显示执行计划
eg：

SQL> explain plan for
2  select * from amy_emp;

Explained.

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

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 320686012

-----------------------------------------------------------------------------
| Id  | Operation         | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |         |    14 |   532 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| AMY_EMP |    14 |   532 |     3   (0)| 00:00:01 |
-----------------------------------------------------------------------------

8 rows selected.

SQL>

2）、DISPLAY_CURSOR:这个函数显示了在加载到内存中的所有cursor执行计划，除此之外还有一些统计信息如（i/0,memory,timing)：

该函数定义：

DBMS_XPLAN.DISPLAY_CURSOR(
sql_id           IN  VARCHAR2  DEFAULT  NULL,
cursor_child_no  IN  NUMBER    DEFAULT  0,
format           IN  VARCHAR2  DEFAULT  'TYPICAL');

eg：

参考：http://docs.oracle.com/cd/E11882_01/appdev.112/e40758/d_xplan.htm#CACFJGHG

我可以在执行完一条语句之后直接使用该函数：

QL> select * from amY_dept where deptno>20;

DEPTNO DNAME          LOC
---------- -------------- -------------
30 SALES          CHICAGO
40 OPERATIONS     BOSTON

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID  8rpwwabhbasvn, child number 0
-------------------------------------
select * from amY_dept where deptno>20

Plan hash value: 3336059312

------------------------------------------------------------------------------
| Id  | Operation         | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |          |       |       |     4 (100)|          |
|*  1 |  TABLE ACCESS FULL| AMY_DEPT |     3 |    60 |     4   (0)| 00:00:01 |
------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - filter("DEPTNO">20)

18 rows selected.

SQL>