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From "dima machlin (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HIVE-7045) Wrong results in multi-table insert aggregating without group by clause
Date Mon, 12 May 2014 14:10:14 GMT
dima machlin created HIVE-7045:
----------------------------------

             Summary: Wrong results in multi-table insert aggregating without group by clause
                 Key: HIVE-7045
                 URL: https://issues.apache.org/jira/browse/HIVE-7045
             Project: Hive
          Issue Type: Bug
    Affects Versions: 0.12.0, 0.10.0
            Reporter: dima machlin


The scenario :

CREATE  TABLE t1 (a int, b int);
CREATE  TABLE t2 (cnt int) PARTITIONED BY (var_name string);

insert into table t1 select 1,1 from asd limit 1;
insert into table t1 select 2,2 from asd limit 1;

from  t1
insert overwrite table t2 partition(var_name='a') select count(a) cnt 
insert overwrite table t2 partition(var_name='b') select count(b) cnt ;

select * from t2;
returns : 
2 a
2 b

as expected.

Setting the number of reducers higher than 1 :

set mapred.reduce.tasks=2;

from  t1
insert overwrite table t2 partition(var_name='a') select count(a) cnt
insert overwrite table t2 partition(var_name='b') select count(b) cnt;

select * from t2;
1	a
1	a
1	b
1	b

Wrong results.

This happens when ever t1 is big enough to automatically generate more than 1 reducers and
without specifying it directly.

adding "group by 1" in the end of each insert solves the problem :

from  t1
insert overwrite table t2 partition(var_name='a') select count(a) cnt group by 1
insert overwrite table t2 partition(var_name='b') select count(b) cnt group by 1;

generates : 
2 a
2 b

This should work without the group by...
The number of rows for each partition will be the amount of reducers.
Each reducer calculated a sub total of the count.





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