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XQuery Selecting and Filtering


The XML Example Document

We will use the "books.xml" document in the examples below (same XML file as in the previous chapters).

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


Selecting and Filtering Elements

As we have seen in the previous chapters, we are selecting and filtering elements with either a Path expression or with a FLWOR expression.

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) specifies a criteria
  • 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 results in iteration. There can be multiple for clauses in the same FLWOR expression.

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

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 at keyword can be used to count the 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>

It is also allowed with more than one in expression in the for clause. Use comma 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 allows variable assignments and it avoids repeating the same expression many times. The let clause does not result in 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 criteria for the result:

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

The order by Clause

The order by clause is used to specify the sort order of the result. Here we want to order 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 is 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>