【Oracle】SQL优化的重要工具 AUTOTRACE

【AUTOTRACE】SQL优化的重要工具--AUTOTRACE
提到SQL优化，不能不提AUTOTRACE的强大功能。使用起来非常便捷，不过在是使用之前，需要做一些配置的工作。简要的描述一下这个过程，供没有使用过的朋友参考。
1.使用sys用户执行plustrce脚本
sys@ora10g> @?/sqlplus/admin/plustrce
sys@ora10g> drop role plustrace;
drop role plustrace
          *
ERROR at line 1:
ORA-01919: role 'PLUSTRACE' does not exist
sys@ora10g> create role plustrace;
Role created.
sys@ora10g> grant select on v_$sesstat to plustrace;
Grant succeeded.
sys@ora10g> grant select on v_$statname to plustrace;
Grant succeeded.
sys@ora10g> grant select on v_$mystat to plustrace;
Grant succeeded.
sys@ora10g> grant plustrace to dba with admin option;
Grant succeeded.
sys@ora10g> set echo off
2.将plustrace授权给public用户，以便保证所有用户都有权使用autotrace功能
sys@ora10g> grant plustrace to public;
Grant succeeded.
3.连接到具体的用户中，这里是sec用户
sys@ora10g> conn sec/sec
Connected.
4.使用“set autotrace”查看autotrace的命令提示
sec@ora10g> set autotrace
Usage: SET AUTOT[RACE] {OFF | ON | TRACE[ONLY]} [EXP[LAIN]] [STAT[ISTICS]]
5.这里演示一种设置方法
sec@ora10g> set autotrace traceonly
sec@ora10g> select * from cat;
20 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 3442307057
--------------------------------------------------------------------------------
| Id  | Operation             | Name   | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |        |   646 | 47804 |    33   (4)| 00:00:01 |
|*  1 |  FILTER  &nbs