presto-main/src/main/java/io/prestosql/sql/planner/optimizations/QueryCardinalityUtil.java/CardinalityExtractorPlanVisitor/visitTopN
class CardinalityExtractorPlanVisitor:        @Override
        public Range<Long> visitTopN(TopNNode node, Void context)
        {
            return applyLimit(node.getSource(), node.getCount());
        }