Group by statistics estimation could be improved by bounding the total number of rows to source table

set hive.stats.fetch.column.stats=true;

create table t1(i int, j int);
alter table t1 update statistics set('numRows'='10000', 'rawDataSize'='18000');
alter table t1 update statistics for column i set('numDVs'='2500','numNulls'='50','highValue'='1000','lowValue'='0');
alter table t1 update statistics for column j set('numDVs'='500','numNulls'='30','highValue'='100','lowValue'='50');

create table t2(i2 int, j2 int);
alter table t2 update statistics set('numRows'='100000000', 'rawDataSize'='10000');
alter table t2 update statistics for column i2 set('numDVs'='10000000','numNulls'='0','highValue'='8000','lowValue'='0');
alter table t2 update statistics for column j2 set('numDVs'='10','numNulls'='0','highValue'='800','lowValue'='-1');

explain select count (1) from t1,t2
	where t1.j=t2.i2 
group by t1.i, t1.j;

Reducer 2
            Reduce Operator Tree:
              Merge Join Operator
                condition map:
                     Inner Join 0 to 1
                keys:
                  0 _col1 (type: int)
                  1 _col0 (type: int)
                outputColumnNames: _col0, _col1
                Statistics: Num rows: 99700 Data size: 797288 Basic stats: COMPLETE Column stats: COMPLETE
                Group By Operator
                  aggregations: count()
                  keys: _col0 (type: int), _col1 (type: int)
                  mode: hash
                  outputColumnNames: _col0, _col1, _col2
                  Statistics: Num rows: 49850 Data size: 797448 Basic stats: COMPLETE Column stats: COMPLETE <==========
                  Reduce Output Operator
                    key expressions: _col0 (type: int), _col1 (type: int)
                    sort order: ++
                    Map-reduce partition columns: _col0 (type: int), _col1 (type: int)
                    Statistics: Num rows: 49850 Data size: 797448 Basic stats: COMPLETE Column stats: COMPLETE
                    value expressions: _col2 (type: bigint)
  .....................