在这个例子中,我们将针对一副数字图像的像素平均色值创建函数索引。
In this example, we create functional indexes on the average color values of the pixels in a digital image.
函数索引不能是内置的代数、指数、对数或十六进制函数。
A functional index cannot be a built-in algebraic, exponential, log, or hex function.
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.
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.
函数索引还会产生额外的函数执行开销。
A functional index incurs the additional cost of function execution.
该查询计划展示了函数索引的使用。
函数索引可以根据用户定义的类型创建。
本文提供了一些有关函数索引的示例。
This article provides several samples of functional indexes.
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.
这说明,在创建或删除函数索引时,执行索引的表中始终持有一个排他锁。
This means that an exclusive lock is always placed on the indexed table while a functional index is being created or dropped.
用于在INSERT和UPDATE操作中构造索引键的键生成器函数。
Key generator function to construct index key during INSERT and UPDATE operations.
本示例展示如何对圆的面积创建函数索引。
This example shows how to create a functional index on the area of a circle.
函数索引对列中的数据进行转换并按照顺序保存转换后的值。
A functional index transforms the data in a column and stores the derived values in sorted order.
函数索引的存储和维护成本较高。
The cost for storage and maintenance of a functional index can be high.
不能针对返回大对象的UDR创建函数索引。
A functional index cannot be created on a UDR that returns a large object.
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.
在XPath例子中,last函数返回最后匹配元素的索引(用在方括号中)。
In the XPath example, the last function returns the index of the last matched element, which you use in square brackets.
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.
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.
创建函数索引的注意事项。
示例:使用r - Tree访问方法的函数索引。
可以用document()函数来创建涉及多个文件的索引或目录。
You can use the document() function to create indices or tables of content that span multiple files.
下面列出了r - Tree函数索引的一些有趣特性。
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.
不过,虽然我认为预定的索引很酷,但这个简单的函数并没有费心去实现它。
However, even though I recognize the coolness of predictive indexing, my simple function does not bother implementing it.
函数索引是一种强大的性能调优工具。
Functional indexes can be a powerful performance tuning tool.
这个文本搜索包和它的相关函数被称为文本搜索引擎,它是专门设计用来执行文本数据的快速检索和自动索引。
This text search package and its associated functions, referred to as the text search engine, is specifically designed to perform fast retrieval and automatic indexing of text data.
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.
图7显示查询响应时间作为表中文档数(范围从1,000到100,000)的函数(不使用索引或索引表)。
Figure 7 shows the query response times as a function of the number of documents in the table, ranging from 1,000 to 100,000 documents (when no indexes or side tables are used).
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.
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