10.6. Let Clauses

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 10.18. A let clause.

for $answer in collection("answers")
let $qid := $answer.question_id
group by $question := $qid
let $count := count($answer)
where $count gt 1
return {
  "question" : $question,
  "count" : $count
}

Results:

{
  "question" : 6183352,
  "count" : 2
}
{
  "question" : 4419499,
  "count" : 2
}
{
  "question" : 37823,
  "count" : 2
}

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

Example 10.19. A let clause reusing the same variable name.

for $answer in collection("answers")
let $qid := $answer.question_id
group by $qid
let $count := count($answer)
where $count gt 1
let $count := sum(
  collection("faqs")
    [ $$.question_id eq $qid ]!size($$.tags)
)
return {
  "question" : collection("faqs")
      [$$.question_id eq $qid].title,
  "count" : $count
}

Results:

{
  "question" : "Find CouchDB docs missing an arbitrary fiel
d",
  "count" : 4
}
{
  "question" : "MySQL and NoSQL: Help me to choose the righ
t one",
  "count" : 4
}
{
  "question" : null,
  "count" : 0
}