通过执行计划优化sql语句，查看执行计划3种方式

1）autotrace 指令    备注：该指令仅能在sqlplus窗口执行操作，plsqldevelope程序下无法执行该指令     (本人已验证该操作)

命令说明：

set autotrace off                        默认值关闭 autotrace

set autotrace on  explain          仅显示执行计划

set autotrace on statistice         显示执行计划统计信息

set autotrace on                        该选项包含 explain  statistice


sql>set autotrace on

sql>select * from epm;

执行计划：

Execution Plan
----------------------------------------------------------
Plan hash value: 3956160932

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


Statistics
----------------------------------------------------------
   0  recursive calls
   0  db block gets
   7  consistent gets
   0  physical reads
   0  redo size
       1630  bytes sent via SQL*Net to client
 523  bytes received via SQL*Net from client
   2  SQL*Net roundtrips to/from client
   0  sorts (memory)
   0  sorts (disk)
  14  rows processed


2）explain plan命令       该指令在plsqldevelope 已经验证


SQL> explain plan for select * from employees;
 
Explained
 
SQL> select * from table(dbms_xplan.display);
 
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 1445457117
-------------------------------------------------------------------------------
| Id  | Operation         | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |           |   107 |  7383 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| EMPLOYEES |   107 |  7383 |     3   (0)| 00:00:01 |
-------------------------------------------------------------------------------
 
8 rows selected


3）使用Toad,PL/SQL Developer工具


     工具没验证


以上文档参考文献：http://blog.chinaunix.net/uid-21187846-id-3022916.html