Let clauses


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JSONiq follows the W3C standard for let clauses. The following explanations, provided as an informal summary for convenience, are non-normative.

Figure 58. LetClause

Let bindings can be used to define aliases for any sequence, for convenience.

For each incoming tuple, the expression in the let clause is evaluated to a sequence. A binding is added from this sequence to the let variable in each tuple. A tuple is hence produced for each incoming tuple.

Example 132. An order by clause.

for $x in collection("captains")
let $century := $x.century
group by $century
let $number := count($x)
where $number gt 1
return { "century" : $century, "count" : $number }

Result (run with Zorba): { "century" : 24, "count" : 4 }

Note that it is perfectly fine to reuse a variable name and hide a variable binding.

Example 133. An order by clause.

for $x in collection("captains")
let $century := $x.century
group by $century
let $number := count($x)
let $number := count(distinct-values(for $series in $x.series
                                     return typeswitch($series)
                                            case array return $series()
                                            default return $series ))
where $number gt 1
return { "century" : $century, "number of series" : $number }

Result (run with Zorba): { "century" : 24, "number of series" : 3 }