set hive.map.aggr = true; -- union case: all subqueries are a map-reduce jobs, 3 way union, same input for all sub-queries, followed by filesink create table tmptable(key string, value int); explain insert overwrite table tmptable select unionsrc.key, unionsrc.value FROM (select 'tst1' as key, count(1) as value from src s1 UNION ALL select 'tst2' as key, count(1) as value from src s2 UNION ALL select 'tst3' as key, count(1) as value from src s3) unionsrc; insert overwrite table tmptable select unionsrc.key, unionsrc.value FROM (select 'tst1' as key, count(1) as value from src s1 UNION ALL select 'tst2' as key, count(1) as value from src s2 UNION ALL select 'tst3' as key, count(1) as value from src s3) unionsrc; select * from tmptable x sort by x.key;