它如何选择在优化存取路径中使用这些策略中的哪一个？
How does it choose which of these strategies to use in the optimized access paths?
在选择访问路径之前，DB 2优化器将sql语句转换成语意上一致的形式，例如使用谓词下推或谓词传递闭包。
Before access path selection, the DB2 optimizer transforms SQL statements into forms that are semantically identical, such as by using predicate pushdown or predicate transitive closure.
SQL编译器使用查询优化来为任何给定的sql语句选择表现最好的访问路径(当然，这要在合理的时间内)。
The SQL compiler USES query optimization to select the best performing access path for any given SQL statement (within a reasonable amount of time, of course).
如果编目中没有列数据值分布信息，DB 2就会假设值是均匀分布的，这可能导致优化器选择非最优的访问路径。
Without column data-value distribution information in the catalog, DB2 will assume an even distribution of values, which may lead the optimizer to a sub-optimal access path.
如果sql语句设计得很糟，优化器就很难转换查询，在选择最佳访问路径时的选择就很少。
If the SQL statement is badly coded, it is difficult for the optimizer to transform the query, leaving fewer options available for choosing an optimal access path.
尽管DB 2优化器对选择最佳访问路径有所帮助，但结果还是依赖于输入数据，优化器无法访问或控制这些数据。
Although the DB2 optimizer is helpful for selecting the best access path, the result depends on the input data, which is often not accessed or controlled by the optimizer.
还有，在选择访问路径之前，优化器首先会执行一系列查询转换以增加可用访问路径的数目。
Also, before selecting the access path, the optimizer first performs a series of query transformations to increase the number of access paths available.
访问计划描述访问路径，这些路径是DB 2优化器为sql语句访问数据而选择的。
Access plan describes the access path that the DB2 optimizer has chosen for accessing data for an SQL statement.
不一致的统计数据还会误导优化器选择糟糕的访问路径。
The inconsistent statistics may also mislead the optimizer into choosing a bad access path.
性能调优的目的是尽可能为优化器提供最好的输入，以便优化器能选择最好的访问路径。
The purpose of query tuning is to provide the best possible input to the optimizer so that the optimizer can choose the best access path.
丢失的统计数据会让优化器高估或低估谓词的选择性，最终会选择低效的访问路径。
Missing statistics can cause the optimizer to overestimate or to underestimate the selectivity of a predicate, and eventually to select an inefficient access path.
如图1所示，DB 2优化器选择最佳访问路径。
As shown in Figure 1, the DB2 optimizer chooses the best access path.
在执行SQL之前，DB 2优化器会评估候选访问路径的成本，然后选择成本最低的路径。
Before SQL is executed, the DB2 optimizer estimates the cost of the candidate access paths and selects the path with the least estimated cost.
但是，首先需要了解DB 2优化器选择的路径。
But first, you need to understand the path selected by the DB2 optimizer.
你不仅需要优化方向，选择好路径，而且你要看清脚下的每一步。
It is required that you should make the right direction and choose the appropriate path, and keep aware of your footstep.
并在优化刀具选择和走刀路径等方面给出了加工过程的优化算法。
The optimized algorithm of machining process about moving route and reamer choice was introduced.
在计划优化模块中，详细讨论了存取路径的选择和代价评估的计算方法。
In plan optimization module, the access path selection and the account method of cost evaluation are discussed in detail.
因此，该参数对于优化基于802.11的无线网格网的路径选择，提高网络性能是行之有效的。
So it is effective on optimizing the path selection of wireless mesh network based on 802.11 and improving the performance of network .
典型的CUBE计算涉及物化策略、物化路径选择与优化方法、CUBE计算方法等三个方面。
Typically, the computation of CUBE consists of materializing strategy, the choice of materialized paths and its optimization and CUBE algorithms.
本文对数据库的查询技术进行分析，给出两种优化方法：分解查询和选择最优存取路径。
In this paper, first the query technology on database is analysed, then two optimization methods are offered: the disintegration query and the best access path selection.
本文基于模糊数学规划及系统优化的观点研究了分组交换网络中分组路径的选择问题。
The problem of route selection of the packets in networks is studied based on the viewpoint of fuzzy mathematical programming and system optimization in this paper.
提供了一种有大量的客户数据，只需对部分客户进行带有时间窗要求的货物配送的优化路径选择算法。
A kind of algorithm is provided to choose the optimized route for freight delivery that involves a great deal of clients' data, but, only deals with a part of them with the request of time Windows.
该算法根据测量邻近点之间的曲率变化关系，优化选择测量点，生成测量路径和DMIS程序。
This algorithm can select appropriate measuring points to create the measuring path and DMIS program according to the curvature relationship between vicinity points.
通过对模型的分析和优化，获得城市疏运最佳路径的选择方式和疏运时间。
By analyzing and optimizing the model, it receives the best evacuation route and time.
对可阶段化运输网络，提出了将路径选择与交通运输方式相结合的组合优化模型。
For transportation networks that can be staging, we suggest a combination optimization model of multiple transportation mode.
本文分析了GIS环境下动态路径优化算法的特点，对GIS环境下城市路网的最优路径选择问题的关键技术进行了研究和验证。
This paper analyses some characters of dynamic path optimum algorithm, studies and verifies the key techniques of the optimum path of city road network under GIS.
本文分析了GIS环境下动态路径优化算法的特点，对GIS环境下城市路网的最优路径选择问题的关键技术进行了研究和验证。
This paper analyses some characters of dynamic path optimum algorithm, studies and verifies the key techniques of the optimum path of city road network under GIS.
应用推荐