Combining queries

Subqueries

Wherever an expression is allowed in AQL, a subquery can be placed. A subquery is a query part that can introduce its own local variables without affecting variables and values in its outer scope(s).

It is required that subqueries be put inside parentheses ( and ) to explicitly mark their start and end points:

FOR p IN persons
  LET recommendations = (
    FOR r IN recommendations
      FILTER p.id == r.personId
      SORT p.rank DESC
      LIMIT 10
      RETURN r
  )
  RETURN { person : p, recommendations : recommendations }

FOR p IN persons
  COLLECT city = p.city INTO g
  RETURN {
    city : city,
    numPersons : LENGTH(g),
    maxRating: MAX(
      FOR r IN g
      RETURN r.p.rating
    )}

Subqueries may also include other subqueries.

Note that subqueries always return a result array, even if there is only a single return value:

RETURN ( RETURN 1 )

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To avoid such a nested data structure, FIRST() can be used for example:

RETURN FIRST( RETURN 1 )

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