朗硕嵌入式无线路由器怎么改密码

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解决时间 2021-02-26 22:13

提问者网友：贪了杯
2021-02-26 08:26

朗硕嵌入式无线路由器怎么改密码

最佳答案

五星知识达人网友：躲不过心动
2021-02-26 09:22

CBO优化器估算的对应谓词的基数与实际的技术差别如下：
表名
估算基数实际基数差别倍数
T2 24167 128 188.80
T3 26045 0 26045
很显然，实际基数与估算的基数差别太大，从而优化器选择了错误的执行路径，正确的执行路径应该是走索引的。究其原因，可以分析下，

dingjun123@ORADB> SELECt COUNT(*) FROM t2 WHERe "T2"."OBJECT_NAME"='T';
Elapsed: 00:00:00.00
Execution Plan
----------------------------------------------------------
Plan hash value: 2583336616
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECt STATEMENT | | 1 | 24 | 3 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 24 | | |
|* 2 | INDEX RANGE SCAN| I2 | 52 | 1248 | 3 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("T2"."OBJECT_NAME"='T')

dingjun123@ORADB> SELECT COUNT(*) FROM t2 WHERe ''='T';
Elapsed: 00:00:00.00
Execution Plan
----------------------------------------------------------
Plan hash value: 402395414
--------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time |
--------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 9411 (1)| 00:01:53 |
| 1 | SORT AGGREGATE | | 1 | | |
|* 2 | FILTER | | | | |
| 3 | TABLE ACCESS FULL| T2 | 2411K| 9411 (1)| 00:01:53 |
--------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------

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