步骤 2.5：验证选择性估计
如果有了准确的统计信息，那么查询优化器一般能够得出正确的选择性估计。
Given accurate statistics, the query optimizer generally comes up with correct selectivity estimates.
然后，这些信息被包括进来，用于帮助优化器在为那些符合条件的查询(这些查询不需要直接引用视图)的选择性估计和基数估计计算成本时做决定。
This information can then be included as part of the optimizer decision during costing for selectivity and cardinality estimates for qualified queries which do not need to reference the view directly.
它们仅针对字符串列进行收集，查询优化器用它们来提高“columnLIKE' %abc '”和“column LIKE ' % abc % '”类型谓词的选择性估计。
They are collected for string columns only, and they are used by the query optimizer to improve the selectivity estimates for predicates of the type "column LIKE '% ABC'" and "column LIKE '% ABC %'".
换句话说，优化器过高估计了本地谓词对表格的选择性。
In other words, the optimizer overestimated the selectivity of the local predicates on the table.
为此，可以在where子句中将关键字SELECTIVITY放在谓词的后面，后面带一个0到1之间的对选择性的估计值。
To that end, you can append the selectivity keyword right after the predicate in the WHERE clause, followed by an estimated or guessed selectivity value in the range of 0 and 1.
研究了频率选择性瑞利衰落信道中的同步MC-CDMA系统上行链路空时信道估计及多用户检测算法。
The space-time channel estimation and multiuser detection algorithm for the uplink of multicarrier CDMA (MC-CDMA) system in frequency selective Rayleigh fading channel were investigated.
对于整数频偏估计，分析了一种基于序列自相关的算法，并将该算法推广应用到频率选择性信道中；
For integer frequency offset estimation, we analyze a sequence auto-correlation based algorithm, and extend the algorithm into frequency selective channel case.
它的另一个特点是具有DOA估计的选择性。
提出一种基于信号子空间估计，用于频率选择性衰落信道的盲多用户自适应接收机。
In this paper, a blind multiuser receiver for frequency-selective fading channel based on subspace tracking has been presented.
频率选择性快衰落信道的精确估计对接收机性能的提高起着重要作用。
The receiver performance can be greatly improved by precisely estimating frequency-selective fast-fading channel information.
验证了把CS(周期平稳过程算法)应用于选择性信道下进行频偏估计的可行性。
Demonstrating the feasibility using CS (Cyclostationary) algorithms to estimate frequency offset in selective channel.
本文首先讨论了移动通信信道的各种参数对信道估计的影响，介绍了频率选择性信道的抽头延迟线模型和分集接收技术，在此基础上阐述了RAKE接收机的原理。
The tapped delay model of the multi-path frequency selective fading channels as well as the diversity receiver technique is introduced, and the principles of RAKE receiver are described.
本文主要研究了基于训练序列的多输入多输出（MIMO）时变频率选择性衰落信道的估计与跟踪问题。
The problem of channel estimation and tracking for MIMO time-varying frequency-selective channels is investigated based on training sequences.
本文仔细研究了在高斯白噪声信道下、频率平坦衰落信道下和频率选择性衰落信道下高精度估计信号载频偏差的问题，并对相应算法提出了一些改进办法。
The problems of carrier frequency offset estimation under the condition of the AGWN channel, frequency flat-fading channel and frequency selective-fading channel are studied in detail respectively.
提出了一种适用于时间频率选择性衰落信道的MIMO - OFDM系统的组合信道估计方法。
A combined channel estimation method of time-frequency-selective fading channels in MIMO-OFDM systems was proposed.
提出了一种适用于时间频率选择性衰落信道的MIMO - OFDM系统的组合信道估计方法。
A combined channel estimation method of time-frequency-selective fading channels in MIMO-OFDM systems was proposed.
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