But the selectivity calculated in this way is not as accurate as selectivity calculated using data distribution.
但是，使用该方式计算的选择性不如使用数据分布计算的选择性准确。
However, in the absence of data distribution information, the optimizer will calculate selectivity for filters of different types based on table indexes.
然而在缺乏数据分布信息的情况下，优化器将基于表索引计算不同类型筛选器的选择性。
The optimizer USES data distribution information generated by UPDATE STATISTICS to calculate selectivity for the filters in the query.
优化器使用UPDATESTATISTICS所生成的数据分布信息来计算查询中筛选器的选择性。
Refer to Chapter 10 of the Performance Guide for the detailed table that the optimizer USES to calculate selectivity in the absence of data distribution.
关于在缺乏数据分布的情况下，优化器用以计算选择性的详细表，请参阅performanceGuide的第10章。
If the data is skewed on the columns, for example if the majority of the data has a city name of Singapore, then the current selectivity could be greatly overestimated.
如果列上的数据有偏离，假设大多数城市名为Singapore，那么当前的选择性可能会被大大高估。
However, in the absence of data distributions, the database server calculates selectivity for filters of different types based on table indexes.
但是，如果没有数据分布，则数据库服务器根据表索引计算不同类型的过滤器的选择率。
The optimizer can use data distributions to calculate selectivity for the filters in a query.
优化器可以使用数据分布来计算查询中过滤器的选择率。
High data transmission rates and high mobility give rise to time - and frequency - selectivity in wireless communication channels.
高数据传输速率以及终端的高速移动，导致无线通信信道具有时间选择性与频率选择性两个特征。
Mechanical test results must be evaluated In conjunction with catalyst activity, selectivity, and stability data.
必须将机械测试结果和催化剂活性、选择性和稳定性数据联系起来进行综合评价。
They give better predicate selectivity estimates for unevenly distributed data.
如果数据不是均匀的，可以给出更好的预测。
They give better predicate selectivity estimates for unevenly distributed data.
如果数据不是均匀的，可以给出更好的预测。
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