presto-main/src/main/java/io/prestosql/sql/planner/optimizations/QueryCardinalityUtil.java/QueryCardinalityUtil/visitEnforceSingleRow
class QueryCardinalityUtil:        @Override
        public Range<Long> visitEnforceSingleRow(EnforceSingleRowNode node, Void context)
        {
            return Range.singleton(1L);
        }