SQL的执行计划-优快云博客

本文通过展示在Windows XP环境下使用Oracle 10g R2进行SQL查询的具体案例，包括设置计时、自动跟踪以及获取执行计划的过程，详细解析了如何评估SQL语句的性能，并提供了执行计划和统计信息。

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* 2008/06/25 星期三
*蒙昭良
*环境：WindowsXP + Oracle10gR2
*SQL的执行计划
*/
SQL> select count(*) from test;

COUNT(*)
----------
     51470

SQL> set timing on
SQL> select count(*) from test;

COUNT(*)
----------
     51470

已用时间: 00: 00: 09.89
SQL> set autotrace on
SQL> select count(*) from test;

COUNT(*)
----------
     51470

已用时间: 00: 00: 03.78

执行计划
----------------------------------------------------------
Plan hash value: 1950795681

-------------------------------------------------------------------
| Id | Operation          | Name | Rows | Cost (%CPU)| Time     |
-------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 | 4107   (1)| 00:00:50 |
|   1 | SORT AGGREGATE    |      |     1 |            |          |
|   2 |   TABLE ACCESS FULL| TEST | 16763 | 4107   (1)| 00:00:50 |
-------------------------------------------------------------------

Note
-----
   - dynamic sampling used for this statement

统计信息
----------------------------------------------------------
          0 recursive calls
          0 db block gets
      15098 consistent gets
      12361 physical reads
          0 redo size
        410 bytes sent via SQL*Net to client
        385 bytes received via SQL*Net from client
          2 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
          1 rows processed

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