for and let clauses

A for or let clause in a FLWOR expression binds one or more variables to values that will be used in other clauses of the FLWOR expression.

for clauses
A for clause iterates through the result of an expression and binds a variable to each item in the sequence.
let clauses
A let clause binds a variable to the entire result of an expression. A let clause does not perform any iteration.
for and let clauses in the same expression
When a FLWOR expression contains both for and let clauses, the variable bindings that are generated by let clauses are added to the variable bindings that are generated by the for clauses.
for and let clauses compared
Although for and let clauses both bind variables, the manner in which variables are bound is different.
Variable scope in for and let clauses
A variable that is bound in a for or let clause is in scope for all of the sub-expressions of the FLWOR expression that appear after the variable binding.

Parent topic: FLWOR expressions

Related reference

FLWOR examples
order by clauses
Syntax of FLWOR expressions