XQuery SUMMARY!
===============
XQuery Introduction
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XQuery (XML Query Language) is a powerful language for querying and manipulating XML data. It is designed to query, transform, and manipulate XML documents, and is used widely in databases, web services, and data integration.
XQuery Example
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A simple XQuery expression can be used to retrieve data from an XML document.
Example XML:
.. code-block:: xml
Harry Potter
J.K. Rowling
29.99
A Brief History of Time
Stephen Hawking
15.50
Example XQuery to select all titles:
.. code-block:: text
for $book in doc("library.xml")//book
return $book/title
This query retrieves the `` element for each `<book>` in the document.
XQuery FLWOR
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FLWOR (For, Let, Where, Order by, Return) is the core expression in XQuery, used for selecting, filtering, and transforming data.
Example of FLWOR expression:
.. code-block:: text
for $book in doc("library.xml")//book
where $book/price > 20
order by $book/title
return <result>
<title>{ $book/title }
{ $book/author }
This selects books with a price greater than 20 and sorts them by title.
XQuery HTML
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XQuery can also be used to generate HTML content from XML data, making it useful for web applications.
Example XQuery to generate HTML:
.. code-block:: text
for $book in doc("library.xml")//book
return
{ $book/title }
Author: { $book/author }
Price: { $book/price }
This will generate an HTML page for each book.
XQuery Terms
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- **For**: Iterates over a set of nodes.
- **Let**: Binds a variable to a value.
- **Where**: Filters the data based on a condition.
- **Order by**: Sorts the results.
- **Return**: Specifies the output.
XQuery Syntax
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XQuery syntax is similar to XPath, but with the added power of variables and operations like `for`, `let`, `where`, `order by`, and `return`.
Basic structure of an XQuery:
.. code-block:: text
for $variable in $sequence
return $expression
Where `$sequence` is a set of XML nodes and `$expression` is what will be returned for each node.
XQuery Add
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XQuery allows you to add new elements or nodes to the XML document.
Example XQuery to add a new book element:
.. code-block:: text
let $newBook :=
New Book
Author Name
25.00
return doc("library.xml")/*,$newBook
This will add the new `` element to the XML document.
XQuery Select
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The `select` clause in XQuery is used to retrieve specific parts of an XML document.
Example XQuery to select books with a price greater than 20:
.. code-block:: text
for $book in doc("library.xml")//book
where $book/price > 20
return $book
XQuery Functions
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XQuery supports various built-in functions like:
- `count()`: Counts the number of nodes.
- `concat()`: Concatenates strings.
- `string-length()`: Returns the length of a string.
Example to count the number of books:
.. code-block:: text
let $bookCount := count(doc("library.xml")//book)
return Number of books: {$bookCount}
This counts the number of `` elements in the XML document and returns it.