XQuery SelectandFilter

XML Example Document

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

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

Selecting and Filtering Elements

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

Look at 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) sets the sort order of the results
  • return - specifies what to return in the result

for statement

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

To loop a specified number of times in a for statement, 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>

Keywordat 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 the for statement. 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 performs variable assignment and can avoid repeating the same expression multiple times. The let statement does not cause iterations.

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 sort order of the results. Here, we will 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 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>
Other Extensions