注意：优化器不会对下面这个查询使用函数索引。
Note: Here is a query for which the optimizer cannot consider using the functional index.
最后，执行查询，该查询将使用函数索引。
这个例子演示了如何使用函数索引选择具有某些特征的图像。
This example demonstrates how functional indexes can be used to select images with certain characteristics.
希望我们介绍的这些创建和使用函数索引的方法能够帮助您改善查询搜索的性能。
Hopefully by seeing the various ways that functional indexes are created and used, you will be able to use them to improve the performance of your query searches.
接下来将深入讨论如何创建和使用函数索引，以及如何生成和检验查询计划，并提供具体的示例。
The in-depth discussion and examples that follow explore creating and using functional indexes and how to generate and examine query plans.
如果表非常小，或者不经常执行使用函数索引的查询，那么创建函数索引可能收效甚微。
If the tables are small or if the frequency of queries that would make use of the functional index is small, then you may not benefit from creating a functional index.
此外，您还将了解如何创建和使用函数索引，以及在创建函数索引之前需要考虑的一些问题。
In addition, you will learn how to create and use functional indexes and be given a list of things to consider before creating functional indexes.
如果数据大小较小，或者索引对于数据库查询的性能改善帮助不大，则不适合使用函数索引。
Indexes won't help much when the size of your data is small or when the majority of queries issued against your database would generally not benefit from an index.
现在，您已了解了函数索引的定义以及其使用方式和使用时机，接下来，将提供一些使用函数索引的例子。
Now that you have learned the definition of a functional index and have seen how and when to use them, below you will find some examples where a functional index is used.
注意：当索引表达式被用于关系表达式，或作为某个操作符类函数的参数时，查询优化器将考虑使用函数索引。
Note: the query optimizer considers using a functional index when the index expression is used in a relational expression or as an argument to one of the operator class functions.
我们需要指定应该使用哪个函数来根据给定的输入值生成索引条目。
We need to specify which function should be used to generate the index entries from the given input value.
该查询计划展示了函数索引的使用。
为了生成索引页，我们将使用4ss的一些扩展函数，以使XSLT访问rdf模型。
To generate an index page, we will use some extension functions of 4ss for XSLT to access the RDF model.
本文的目的是帮助您理解函数索引的定义以及使用。
The purpose of this article is to help you understand what functional indexes are and how they are used.
如果将某个UDR用于函数索引，则该U DR不能使用集合数据类型作为参数类型。
A UDR used by a functional index cannot have arguments that are collection data types.
NetSearchExtender并不使用字符串匹配连续地搜索文本数据(就像XQuerycontains函数所做的那样)，而是使用文本索引。
Rather than sequentially searching through the text data using string matching, as done with the XQuery contains function, Net search Extender USES a text index.
Substring函数使用一个分隔符和索引来判断要从进入的源字符串提取哪些文本。
The Substring function uses a delimiter and index to determine what text to extract from the incoming source string.
使用Devhelp，可以迅速地搜索函数索引并浏览已经安装的文档，从而可以更迅速地获得需要的信息。
Using Devhelp, you can instantly search a function index and browse the installed documentation, allowing you to obtain needed information much more rapidly.
具体来说，我们将使用名为tokenextraction的主索引函数的附带行为。
Specifically, we'll use a collateral behavior of the main indexing function called token extraction.
如果像前面建议的那样，使用数组索引从actiontransitionfunctions表直接调用函数，this变量就会指向这个表。
If you actually called the function directly from the actionTransitionFunctions table using array indexes, as suggested earlier, the this variable would point into the table.
这个方法使用当前状态和事件类型作为关联数组的索引，从actionTransitionFunctions表中选择要调用的函数。
The method does select a function to call from the actionTransitionFunctions table using the current state and event type as associative array indexes.
在本例中，我们将向您展示如何创建使用r - Tree访问方法的函数索引。
In this example we show you how to create a functional index that USES the R-Tree access method.
SELECT查询在查询过滤器中指定图像处理函数，现在，这些查询的运行速度得到了提高，因为它们使用索引判断每个元组(tuple)是否满足查询。
SELECT queries that specify image processing functions in their query filters now run faster because they use the index to determine whether or not each tuple satisfies the query.
要想避免使用fn：upper - case函数并利用xml索引加快查询，就需要创建不区分大小写的数据库。
To avoid the use of the fn: upper-case function and exploit the benefits of XML indexes, it is necessary to create a case-insensitive database.
这说明，该函数必须在一个涉及比较操作并且引用了索引扩展hash _ index的搜索方法“equals”的表达式中使用。
It says that the function must be used in an expression involving the comparison operation and that the search method "equals" of the index extension hash_index is referred to.
使用第一种方法，您可以通过syscall函数调用由其索引所标识的新函数。
With the first method, you call your new functions as identified by their index through the syscall function.
使用syscall函数，您可以通过指定它的调用索引和一组参数来调用系统调用。
With the syscall function, you can call a system call by specifying its call index and a set of arguments.
这听起来好像有一大堆的条件，但还是比较简单的：通过使用列可以找到索引，通过使用函数可以知道空间谓词。
This sounds like a lot of conditions, but so far it is straightforward: using the column, the index can be found and the spatial predicate is known using the function.
该查询计划显示索引扫描使用了函数索引。
This query plan shows an index scan using our functional index.
您已经了解了函数索引的定义以及其使用方式和使用时机。
You have now learned the definition of a functional index and have seen how and when to use them.
应用推荐