FLWOR expressions

FLWOR (pronounced flower) expressions are the most common expressions in XQuery. They are similar to select-from-where statements in SQL. The name FLWOR is an acronym, standing for the first letter of the clauses that may occur in such an expression:

for

for clauses associate one or more variables to XQuery expressions. Each variable iteratively is bound to one value of the corresponding expression.

let

let clauses bind variables to the entire result of an XQuery expression. A sequence of variable bindings created by for and let clauses of a FLWOR expression is called a tuple.

where

where clauses filter tuples retaining only those that satisfy a given condition;

order by

order by clauses sort tuples according to the given criteria;

return

return clauses build the result of the expression.

A FLWOR expression starts with one or more for or let clauses in any order, followed by an optional where clause, followed by an optional order by clause, followed by a required return clause.