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 2 map-reduce subqueries is performed followed by select and a file sink -- However, all the columns are not selected. So, union cannot -- be removed. -- 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. The union is removed, the select (which changes the order of -- columns being selected) is pushed above the union. create table inputTbl1(key string, val string) stored as textfile; create table outputTbl1(key string) stored as textfile; load data local inpath '../../data/files/T1.txt' into table inputTbl1; explain insert overwrite table outputTbl1 SELECT a.key FROM ( SELECT key, count(1) as `values` from inputTbl1 group by key UNION ALL SELECT key, count(1) as `values` from inputTbl1 group by key ) a; insert overwrite table outputTbl1 SELECT a.key FROM ( SELECT key, count(1) as `values` from inputTbl1 group by key UNION ALL SELECT key, count(1) as `values` from inputTbl1 group by key ) a; desc formatted outputTbl1; set hive.input.format=org.apache.hadoop.hive.ql.io.HiveInputFormat; select * from outputTbl1 order by key;