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XML XQuery Introduction

  • XQuery is a language used for querying and manipulating data in XML format.
  • It is a powerful and expressive language that allows developers to retrieve and transform data using a variety of functions and operators.

Syntax

The basic syntax of XQuery is as follows:

for $variable in /path/to/node
where $variable/condition
return $variable/data

The keyword for is used to define the variable, followed by the variable name and the path to the XML node. The where keyword is used to specify a condition for the variable, and the return keyword is used to specify the data to be retrieved.

Example

Consider the following XML document:

<employees>
    <employee id="1">
        <name>John</name>
        <age>30</age>
    </employee>
    <employee id="2">
        <name>Jane</name>
        <age>25</age>
    </employee>
</employees>

To retrieve the names of all employees who are over the age of 28, we can use the following XQuery:

for $employee in /employees/employee
where $employee/age > 28
return $employee/name

The output of the above query would be:

John

Explanation

In the above example, we use the for keyword to define the variable $employee and set its value to the path /employees/employee. We then use the where keyword to specify a condition for the variable - in this case, we only want to retrieve data for employees whose age is greater than 28. Finally, we use the return keyword to specify the data to be retrieved - in this case, we want to retrieve the names of the matching employees.

Use

XQuery is commonly used for retrieving data from large XML documents, where traditional methods like XPath and XSLT may not be efficient enough. It is also used for transforming XML data into other formats, such as HTML, CSV, or JSON.

Important Points

  • XQuery is a declarative language, which means that it focuses on specifying what you want to do with the data, not how to do it.
  • XQuery is based on XPath, so developers familiar with XPath will find it easy to learn.
  • XQuery supports a wide range of functions and operators, making it a powerful language for data manipulation.

Summary

XQuery is a powerful language for querying and manipulating XML data. Its declarative syntax and support for a wide range of functions and operators make it a popular choice among developers working with large XML documents.

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