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XML Example Document

We will continue using the "books.xml" document in the examples below (the same XML file used in the previous chapter). View the "books.xml" file in your browser.

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Selecting and Filtering Elements

As seen in previous chapters, we use path expressions or FLWOR expressions to select and filter elements.

Consider the following FLWOR expression:

for $x in doc("books.xml")/bookstore/book

 where $x/price>30

 order by $x/title

 return $x/title

• for - (optional) binds a variable to each item returned by the in expression
• let - (optional)
• where - (optional) sets a condition
• order by - (optional) specifies the sort order of the result
• return - specifies what to return in the result

The for Clause

The for clause binds a variable to each item returned by the in expression. The for clause enables iteration. Multiple for clauses can exist within the same FLWOR expression.

To loop a specific number of times in a for clause, you can use the keyword to:

for $x in (1 to 5)

 return <test>{$x}</test>

Result:

<test>1</test>

<test>2</test>

<test>3</test>

<test>4</test>

<test>5</test>

The keyword at can be used to count iterations:

for $x at $i in doc("books.xml")/bookstore/book/title

 return <book>{$i}. {data($x)}</book>

Result:

<book>1. Everyday Italian</book>

<book>2. Harry Potter</book>

<book>3. XQuery Kick Start</book>

<book>4. Learning XML</book>

Multiple in expressions are also allowed in a for clause. Use commas to separate each in expression:

for $x in (10,20), $y in (100,200)

 return <test>x={$x} and y={$y}</test>

Result:

<test>x=10 and y=100</test>

<test>x=10 and y=200</test>

<test>x=20 and y=100</test>

<test>x=20 and y=200</test>

The let Clause

The let clause assigns values to variables and helps avoid repeating the same expression multiple times. The let clause does not cause iteration.

let $x := (1 to 5)

 return <test>{$x}</test>

Result:

<test>1 2 3 4 5</test>

The where Clause

The where clause is used to specify one or more conditions (criteria) for the result.

where $x/price>30 and $x/price<100

The order by Clause

The order by clause specifies the sort order of the result. Here, we sort the result by category and title:

for $x in doc("books.xml")/bookstore/book

 order by $x/@category, $x/title

 return $x/title

Result:

<title lang="en">Harry Potter</title>

<title lang="en">Everyday Italian</title>

<title lang="en">Learning XML</title>

<title lang="en">XQuery Kick Start</title>

The return Clause

The return clause specifies what to return.

for $x in doc("books.xml")/bookstore/book

 return $x/title

Result:

<title lang="en">Everyday Italian</title>

<title lang="en">Harry Potter</title>

<title lang="en">XQuery Kick Start</title>

<title lang="en">Learning XML</title>