Yin Huai created HIVE-4781:
------------------------------
Summary: LEFT SEMI JOIN generates wrong results when
Key: HIVE-4781
URL: https://issues.apache.org/jira/browse/HIVE-4781
Project: Hive
Issue Type: Bug
Affects Versions: 0.12.0
Reporter: Yin Huai
Assignee: Yin Huai
Suppose that we have a query shown below
{code:sql}
SELECT key FROM t1 LEFT SEMI JOIN t2 ON (t1.key=t2.key);
{\code}
When the number of rows of t2 is larger than hive.join.emit.interval,
JoinOperator will emit rows from t1, which will result in redundant output.
Let's say t1 is
{code}
key
----
1
{\code}
and t2 is
{code}
key
----
1
1
1
1
{\code}
When hive.join.emit.interval=1, the output of above query will be
{code}
1
1
1
1
{\code}
The correct result should be
{code}
1
{\code}
This problem cannot be found in unit test. Because there is a GBY operator
inserted before JoinOperator and we have only 1 mapper, the output of map phase
only has distinct keys.
Please apply the patch 'wrong_semi_join.txt' attached below and use
{code}
ant test -Dtestcase=TestMinimrCliDriver -Dqfile="left_semi_join.q"
-Dtest.silent=false
{\code} to replay the problem. The wrong result can be found in
{code}
<hive_root_dir>/build/ql/test/logs/clientpositive
{\code}
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