set hive.stats.autogather=false; set hive.optimize.union.remove=true; set hive.mapred.supports.subdirectories=true; set hive.merge.sparkfiles=false; set hive.merge.mapfiles=false; set hive.merge.mapredfiles=false; set mapred.input.dir.recursive=true; -- This is to test the union->selectstar->filesink optimization -- Union of 3 subqueries is performed (exactly one of which requires a map-reduce job) -- followed by select star and a file sink. -- There is no need to write the temporary results of the sub-queries, and then read them -- again to process the union. The union can be removed completely. -- The final file format is different from the input and intermediate file format. -- It does not matter, whether the output is merged or not. In this case, merging is turned -- off -- INCLUDE_HADOOP_MAJOR_VERSIONS(0.23) -- Since this test creates sub-directories for the output table outputTbl1, it might be easier -- to run the test only on hadoop 23 create table inputTbl1(key string, val string) stored as textfile; create table outputTbl1(key string, `values` bigint) stored as rcfile; load data local inpath '../../data/files/T1.txt' into table inputTbl1; explain insert overwrite table outputTbl1 SELECT * FROM ( SELECT key, count(1) as `values` from inputTbl1 group by key UNION ALL SELECT key, 1 as `values` from inputTbl1 UNION ALL SELECT key, 2 as `values` from inputTbl1 ) a; insert overwrite table outputTbl1 SELECT * FROM ( SELECT key, count(1) as `values` from inputTbl1 group by key UNION ALL SELECT key, 1 as `values` from inputTbl1 UNION ALL SELECT key, 2 as `values` from inputTbl1 ) a; desc formatted outputTbl1; set hive.input.format=org.apache.hadoop.hive.ql.io.HiveInputFormat; select * from outputTbl1 order by key, `values`;