XQuery FLWOR Expressions
What is FLWOR?
FLWOR (pronounced "flower") is an acronym for "For, Let, Where, Order by, Return".
- For - selects a sequence of nodes
- Let - binds a sequence to a variable
- Where - filters the nodes
- Order by - sorts the nodes
- Return - what to return (gets evaluated once for every node)
The XML Example Document
We will use the "books.xml" document in the examples below (same XML file as in the previous chapter).
View the "books.xml" file in your browser.
How to Select Nodes From "books.xml" With FLWOR
Look at the following path expression:
doc("books.xml")/bookstore/book[price>30]/title
The expression above will select all the title elements under the book elements that are under the bookstore element that have a price element with a value that is higher than 30.
The following FLWOR expression will select exactly the same as the path expression above:
for $x in doc("books.xml")/bookstore/book
where $x/price>30
return $x/title
The result will be:
<title lang="en">XQuery Kick Start</title>
<title lang="en">Learning XML</title>
With FLWOR you can sort the result:
for $x in doc("books.xml")/bookstore/book
where $x/price>30
order by $x/title
return $x/title
The for clause selects all book elements under the bookstore element into a variable called $x.
The where clause selects only book elements with a price element with a value greater than 30.
The order by clause defines the sort-order. Will be sort by the title element.
The return clause specifies what should be returned. Here it returns the title elements.
The result of the XQuery expression above will be:
<title lang="en">Learning XML</title>
<title lang="en">XQuery Kick Start</title>