FLWOR

FLWOR is an acronym for for, let, where, order by, return. It is a core construct in XQuery and related XML query languages used to transform and assemble sequences from existing data. FLWOR expressions combine iteration, binding of intermediate results, filtering, sorting, and construction in a single, declarative form.

The for clause binds a variable to each item in a source sequence, effectively enabling iteration. The let clause binds a variable to the result of an expression, allowing intermediate computations to be reused within the same FLWOR. The where clause filters the current set of bindings using predicates. The order by clause sorts the resulting items according to one or more expressions. The return clause defines the final output for each combination of bindings, which may be a node, a value, or a constructed fragment.

FLWOR expressions can contain multiple for and let clauses and can nest within other FLWOR expressions. Evaluation proceeds from left to right, with each binding visible to subsequent clauses. Where and order by operate on the active bindings, and return produces the final sequence.

FLWOR is widely used for querying and constructing XML data, enabling concise expressions that map, filter, sort, and restructure data. It is a standard feature in XQuery 1.0 and later versions, and remains a fundamental tool for developers working with XML databases and processing pipelines.