presto-main/src/main/java/io/prestosql/sql/planner/iterative/rule/SingleDistinctAggregationToGroupBy.java/SingleDistinctAggregationToGroupBy/hasSingleDistinctInput
class SingleDistinctAggregationToGroupBy:    private static boolean hasSingleDistinctInput(AggregationNode aggregationNode)
    {
        return extractArgumentSets(aggregationNode)
                .count() == 1;
    }