我是Oracle 11g的新手,我对执行计划有一个问题。我运行了一个查询,即使查询中没有ORDER BY子句,执行计划的统计信息仍然显示内存中有6种排序。有人可以向我解释为什么会这样吗?以下是查询和统计信息:
SQL> SELECT ZIP FROM NOZIPSORT WHERE ZIP BETWEEN '10000' AND '29999' AND rownum < 26;
25 rows selected.
Elapsed: 00:00:00.07
Execution Plan
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Plan hash value: 4176934817
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| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 25 | 150 | 2 (0)| 00:00:01 |
|* 1 | COUNT STOPKEY | | | | | |
|* 2 | TABLE ACCESS FULL| NOZIPSORT | 28 | 168 | 2 (0)| 00:00:01 |
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Predicate Information (identified by operation id):
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1 - filter(ROWNUM<26)
2 - filter("ZIP"<='29999' AND "ZIP">='10000')
Statistics
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311 recursive calls
0 db block gets
47 consistent gets
38 physical reads
520 redo size
805 bytes sent via SQL*Net to client
431 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
6 sorts (memory)
0 sorts (disk)
25 rows processed
答案 0 :(得分:3)
我会说这将是正在进行某些排序的递归调用 - 例如解析查询时,需要查询数据字典以检查表和列定义,其中一些查询将涉及DISTINCT或其他需要排序的操作。