
cts.sumAggregate( range-index as cts.reference, [options as String[]], [query as cts.query?], [forest-ids as (Number|String)[]] ) as xs.anyAtomicType?
  Returns the sum of the values given a value lexicon.
  This function works like cts:sum except it performs the
  calculation in parallel in all data nodes then aggregates the values.
  It generally performs better than cts:sum, especially on
  large clusters.
//   This query assumes an element range index is configured
//   in the database for the 'Amount' element.
cts.sumAggregate(cts.elementReference(xs.QName("Amount")));
=> 733.7600000000000128