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https://issues.apache.org/jira/browse/HIVE-4781?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Yin Huai updated HIVE-4781:
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Attachment: wrong_semi_join.txt
> 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
> Attachments: wrong_semi_join.txt
>
>
> 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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