set hive.map.aggr=true;
set hive.groupby.skewindata=false;

explain
select count(1), count(distinct x.value), count(distinct substr(x.value, 5)) from src x where x.key = 9999;

select count(1), count(distinct x.value), count(distinct substr(x.value, 5)) from src x where x.key = 9999;

set hive.map.aggr=false;
set hive.groupby.skewindata=false;

explain
select count(1), count(distinct x.value), count(distinct substr(x.value, 5)) from src x where x.key = 9999;

select count(1), count(distinct x.value), count(distinct substr(x.value, 5)) from src x where x.key = 9999;