在前面的章节已经介绍了如何使用autotrace，下面我们简单学习如何结合autotrace来分析表。
SQL> analyze table test compute statistics;
——只有执行分析语句时，oracle才会对数据进行基于成本的分析，否则就会按照oracle的优先原则来分析表
——如果不想每次都分析表这么麻烦，就修改optimizer_mode这个参数
SQL> alter system set optimizer_mode=all_rows;---选择优化器的模式
Table analyzed.
SQL> set autotrace on
SQL> select * from test where rownum=1;
        ID NAME                              SEX
---------- ----------------------------- ------------
         1 user1                             M

Execution Plan
----------------------------------------------------------
Plan hash value: 3931117773
---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 |    14 |     2   (0)| 00:00:01 |
|*  1 |  COUNT STOPKEY     |      |       |       |            |          |
|   2 |   TABLE ACCESS FULL| TEST |     1 |    14 |     2   (0)| 00:00:01 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter(ROWNUM=1)

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