Other considerations for access path selection.
选择访问路径的其他影响因素。
Access path selection: What did DB2 decide, and why?
选择访问路径：DB 2做出什么决策？为什么？
Create a temporary keyed access path during execution.
在执行过程中创建临时的关键访问路径。
The access path of the query: How are the tables accessed?
查询的访问路径：如何访问这些表？
Index design has a critical impact on access path selection.
索引设计对访问路径选择至关重要。
The SQL statement itself also impacts the access path selection.
sql语句本身也会影响访问路径选择。
As shown in Figure 1, the DB2 optimizer chooses the best access path.
如图1所示，DB 2优化器选择最佳访问路径。
The SQL statement in Listing 3 creates the access path graph shown in Figure 3.
清单3中的SQL语句创建如图 3所示的访问路径图
The SQL statement in Listing 8 creates the access path graph shown in Figure 8.
清单8中的sql语句创建如图8所示的访问路径图。
The SQL statement in Listing 5 creates the access path graph shown in Figure 5.
清单5中的sql语句创建如图5所示的访问路径图。
The SQL statement in Listing 4 creates the access path graph shown in Figure 4.
清单4中的sql语句创建如图4所示的访问路径图。
The SQL statement in Listing 6 creates the access path graph shown in Figure 6.
清单6中的sql语句创建如图6所示的访问路径图。
To see the table descriptor, right-click the table node in the access path graph.
为了查看表描述符，请右键单击访问路径图上的表节点。
However, for this example a different access path is selected, which is shown in Figure 7.
然而，对于此示例则选择了一个不同的访问路径，如图7所示。
The inconsistent statistics may also mislead the optimizer into choosing a bad access path.
不一致的统计数据还会误导优化器选择糟糕的访问路径。
This type of access path is referred to as a nested loop join (NLJOIN) with sort composite.
这种类型的访问路径被称为使用复合排序的嵌套循环联接(NLJOIN)。
So, any interruption to one of the access path does not affect storage access from the host.
因此，其中一条访问路径的中断不会影响从主机发起的存储访问。
Keep in mind that this catalog data is what the optimizer USES to make access path decisions.
请记住，优化器使用编目数据决定访问路径。
This article described the basic concepts of access paths and how to read an access path graph.
本文描述了访问路径的基本概念以及如何解读访问路径图。
There is no FETCH or table node shown in the access path graph because it is an index-only scan.
因为其是一个唯一索引扫描，所以在访问路径图中不显示FETCH或表节点。
It does this by performing some work ahead of time, such as determining the database access path.
具体表现就是提前执行一些工作，比如确定数据库访问路径。
With the appropriate access path, the ORDER BY or GROUP BY requirement can be met without sorting.
使用恰当的访问路径，无需排序即可满足ORDERBY或GROUP BY需求。
This tells me that I may have an inefficient access path, where DB2 reads more data than it should.
这就说明我可能有一个低效的访问路径，DB 2读取的数据比应该读取的数据更多。
That simple step could lead to a new access path that might dramatically improve query performance.
这个简单的步骤可能产生新的访问路径，可能显著改进查询性能。
Assuming this to be the case, the underlying access path is considered optimal with high confidence.
假设这是事实，基础访问路径会被认为具有最佳的高可信度。
For simplicity, this article refers to a particular way of satisfying an SQL statement as the access path.
为简单起见，本文引用了一种满足sql语句的流行方法作为访问路径。
As you'll see shortly, DB2 can use both of these indexes to generate an efficient access path for our query.
正如您马上就会看到的，DB 2可以使用这两个索引来为我们的查询产生一个高效的访问路径。
Therefore, if the optimizer's estimate is accurate, this access path should be a very efficient access path.
因此，如果优化器的估计是准确的，则此访问路径应该是一个非常有效的访问路径。
You can obtain the statistics from the table descriptor of the table node in the underlying access path graph.
您可以从基础访问路径图中的表节点的表描述符处获得该统计信息。
Then it will either pick the cheapest access path or (as of DB2 10) a slightly more costly but less risky path.
然后它会选取代价最小（对DB210 而言）或是代价稍大但风险较小的路径。
应用推荐