code: func (builder *Builder) Aggregate(q grimoire.Query) (string, []interface{}) {
  	qs, args := builder.query(q)
  	field := q.AggregateMode + "(" + q.AggregateField + ") AS " + q.AggregateMode
  
  	return builder.fields(false, append(q.GroupFields, field)...) + qs, args
  }
docs: // Aggregate generates query for aggregation.