Oracle 执行计划说明
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 onexplain 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 explainstatistice
sql>set autotrace on
sql>select * from epm;
执行计划：
Execution Plan
----------------------------------------------------------
Plan hash value: 3956160932
--------------------------------------------------------------------------
|> --------------------------------------------------------------------------
| 0 | SELECT STATEMENT|| 14 | 532 | 3 (0)| 00:00:01 |
| 1 |TABLE ACCESS FULL| EMP| 14 | 532 | 3 (0)| 00:00:01 |
--------------------------------------------------------------------------
Statistics
----------------------------------------------------------
0recursive calls
0db block gets
7consistent gets
0physical reads
0redo> 1630bytes sent via SQL*Net to client
523bytes received via SQL*Net from client
2SQL*Net roundtrips to/from client
0sorts (memory)
0sorts (disk)
14rows 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
-------------------------------------------------------------------------------
|> -------------------------------------------------------------------------------
| 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
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