What is XQuery?
- XQuery is the language for querying XML data
- XQuery for XML is like SQL for databases
- XQuery is built on XPath expressions
- XQuery is supported by all the major database engines (IBM, Oracle, Microsoft, etc.)
Functions
doc("books.xml")
doc("books.xml")/bookstore/book/title
doc("books.xml")/bookstore/book[price<30]
doc("books.xml")/bookstore/book[price>30]/title
for $x in doc("books.xml")/bookstore/book
where $x/price>30
order by $x/title
return $x/title
<ul>
{
for $x in doc("books.xml")/bookstore/book/title
order by $x
return <li>{$x}</li>
}
</ul>
<ul>
{
for $x in doc("books.xml")/bookstore/book/title
order by $x
return <li>{data($x)}</li>
}
</ul>
doc("books.xml")/bookstore/book/title
doc("books.xml")/bookstore/book[price<30]
doc("books.xml")/bookstore/book[price>30]/title
for $x in doc("books.xml")/bookstore/book
where $x/price>30
order by $x/title
return $x/title
<ul>
{
for $x in doc("books.xml")/bookstore/book/title
order by $x
return <li>{$x}</li>
}
</ul>
<ul>
{
for $x in doc("books.xml")/bookstore/book/title
order by $x
return <li>{data($x)}</li>
}
</ul>
XQuery Basic Syntax Rules
Some basic syntax rules:- XQuery is case-sensitive
- XQuery elements, attributes, and variables must be valid XML names
- An XQuery string value can be in single or double quotes
- An XQuery variable is defined with a $ followed by a name, e.g. $bookstore
- XQuery comments are delimited by (: and :), e.g. (: XQuery Comment :)
XQuery Basic Syntax Rules
for $x in doc("books.xml")/bookstore/book
return if ($x/@category="CHILDREN")
then <child>{data($x/title)}</child>
else <adult>{data($x/title)}</adult>
return if ($x/@category="CHILDREN")
then <child>{data($x/title)}</child>
else <adult>{data($x/title)}</adult>
In XQuery there are two ways of comparing values.
1. General comparisons: =, !=, <, <=, >, >=2. Value comparisons: eq, ne, lt, le, gt, ge
$bookstore//book/@q > 10
The expression above returns true if any q attributes have values greater than 10.
$bookstore//book/@q gt 10
The expression above returns true if there is only one q attribute returned by the expression, and its value is greater than 10. If more than one q is returned, an error occurs.
(: Adding Elements and Attributes to the Result :)
<html>
<body>
<h1>Bookstore</h1>
<ul>
{
for $x in doc("books.xml")/bookstore/book
order by $x/title
return <li class="{data($x/@category)}">{data($x/title)}</li>
}
</ul>
</body>
</html>
(: XQuery Selecting and Filtering :)
for $x in doc("books.xml")/bookstore/book
where $x/price>30
order by $x/title
return $x/title
for $x in (1 to 5)
return <test>{$x}</test>
for $x at $i in doc("books.xml")/bookstore/book/title
return <book>{$i}. {data($x)}</book>
for $x in (10,20), $y in (100,200)
return <test>x={$x} and y={$y}</test>
let $x := (1 to 5)
return <test>{$x}</test>
(:XQuery Built-in Functions :)
<name>{uppercase($booktitle)}</name>
doc("books.xml")/bookstore/book[substring(title,1,5)='Harry']
(: XQuery User-Defined Functions
Syntax :)
declare function prefix:function_name($parameter AS datatype)
AS returnDatatype
{
(: function code here :)
};
declare function local:minPrice(
$price as xs:decimal?,
$discount as xs:decimal?)
AS xs:decimal?
{
let $disc := ($price * $discount) div 100
return ($price - $disc)
};
(: Below is an example of how to call the function above :)
<minPrice>{local:minPrice($book/price, $book/discount)}</minPrice>
let $name := (substring($booktitle,1,4))
<html>
<body>
<h1>Bookstore</h1>
<ul>
{
for $x in doc("books.xml")/bookstore/book
order by $x/title
return <li class="{data($x/@category)}">{data($x/title)}</li>
}
</ul>
</body>
</html>
(: XQuery Selecting and Filtering :)
for $x in doc("books.xml")/bookstore/book
where $x/price>30
order by $x/title
return $x/title
for $x in (1 to 5)
return <test>{$x}</test>
for $x at $i in doc("books.xml")/bookstore/book/title
return <book>{$i}. {data($x)}</book>
for $x in (10,20), $y in (100,200)
return <test>x={$x} and y={$y}</test>
let $x := (1 to 5)
return <test>{$x}</test>
(:XQuery Built-in Functions :)
<name>{uppercase($booktitle)}</name>
doc("books.xml")/bookstore/book[substring(title,1,5)='Harry']
(: XQuery User-Defined Functions
Syntax :)
declare function prefix:function_name($parameter AS datatype)
AS returnDatatype
{
(: function code here :)
};
declare function local:minPrice(
$price as xs:decimal?,
$discount as xs:decimal?)
AS xs:decimal?
{
let $disc := ($price * $discount) div 100
return ($price - $disc)
};
(: Below is an example of how to call the function above :)
<minPrice>{local:minPrice($book/price, $book/discount)}</minPrice>
let $name := (substring($booktitle,1,4))
* Reference to W3C Schools
