XQuery Selection and Filtering

XML instance document

We will continue to use this "books.xml" document (the same as the XML file used in the previous chapters) in the following examples.

View the "books.xml" file in your browser.

Select and filter elements

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

Please see 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) Bind a variable to each item returned by an in expression
let
(Optional)
where
(Optional) Set a condition
order by
(Optional) Set the order of the results
return
Specify the content to be returned in the result

for statement

The for statement binds a variable to each item returned by an in expression. The for statement can produce iteration. Multiple for statements can exist within the same FLWOR expression.

If you need to loop a specified number of times within a for statement, you can usekeywords 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>

Keyword at It can be used to calculate iteration:

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>

Similarly in the for statementMultiple in expressions are allowed. Please 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>

Let statement

The let statement can perform variable assignment and can avoid repeated expressions. The let statement does not cause iteration.

let $x := (1 to 5)
return <test>{$x}</test>

Result:

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

Where statement

The where statement is used to set one or more conditions (criteria) for the results.

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

Order by statement

The order by statement is used to specify the order of the results. Here, we want to sort the results 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>

Return statement:

The return statement specifies the content to be returned.

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>