FLWOR explained

The programming language XQuery defines FLWOR (pronounced 'flower') as an expression that supports iteration and binding of variables to intermediate results. FLWOR is an acronym: FOR, LET, WHERE, ORDER BY, RETURN.^[1] FLWOR is loosely analogous to SQL's SELECT-FROM-WHERE and can be used to provide join-like functionality to XML documents.

for creates a sequence of nodes
let binds a sequence to a variable
where filters the nodes on a boolean expression
order by sorts the nodes
return gets evaluated once for every node

Example

for $d in doc("depts.xml")//deptno let $e := doc("emps.xml")//employee[deptno = $d] where count($e) >= 10 order by avg($e/salary) descending return

First column of the XQuery request shows the for, let, where, order by and return keywords of the FLWOR paradigm. In plain English, this could be read as "Get all departments that have more than ten employees, order these departments by decreasing average salary, and return a report of department numbers, head counts and average salary in each big department". The result could look like: 17 25 12500 24 18 11327 3 32 10725

Example using Microsoft SQL Server

DECLARE @xml XML

SET @xml = '
42 27

a b
'

SELECT x.y.query('for $s in self::node return $s//item_1/text') as i, x.y.query('for $s in self::node return $s//item_2/text') as j FROM @xml.nodes('/root_element') AS x(y);

External links

W3C XML Query (XQuery) - FLWOR Expressions
FLWOR examples
Introduction to FLWOR
https://web.archive.org/web/20111008001258/http://w3schools.com/xquery/xquery_flwor.asp

Notes and References

Book: Walmsley, Priscilla . 2007 . XQuery . Sebastopol, CA, USA . O'Reilly Media . 73 . 978-0-596-00634-1.