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https://issues.apache.org/jira/browse/HIVE-21322?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16777632#comment-16777632
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Vineet Garg commented on HIVE-21322:
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This looks like an issue with nway merge join.
[~norvellj] Can you check if disabling nway merge {{set
hive.merge.nway.joins=false}} fixes this?
> Multiple table LEFT OUTER JOIN results are incorrect when 'is not null' used
> in WHERE clause.
> ---------------------------------------------------------------------------------------------
>
> Key: HIVE-21322
> URL: https://issues.apache.org/jira/browse/HIVE-21322
> Project: Hive
> Issue Type: Bug
> Components: CBO
> Affects Versions: 2.3.4
> Environment: Hive 2.3.4 (emr-5.21.0)
> Reporter: James Norvell
> Priority: Minor
> Attachments: explain-plans.txt
>
>
> Reproduction:
> Create tables:
> {code:java}
> create table a (id string); insert into a values (1),(2),(3);
> create table b (id string, name string); insert into b values
> (1,'a'),(2,'b'),(3,null);
> create table c (id string); insert into c values (11),(22),(33);
> {code}
> When joining a -> b -> c on id, the following query is correct:
> {code:java}
> select a.id, b.name from a
> left outer join b on a.id = b.id
> left outer join c on a.id = c.id
> where b.name is not null;
> OK
> 1 a
> 2 b
> Time taken: 10.231 seconds, Fetched: 2 row(s)
> {code}
> Switching the join order from a -> c -> b results in incorrect results:
> {code:java}
> select a.id, b.name from a
> left outer join c on a.id = c.id
> left outer join b on a.id = b.id
> where b.name is not null;
> OK
> 2 b
> Time taken: 10.321 seconds, Fetched: 1 row(s)
> {code}
> Disabling hive.cbo.enable or changing execution engine to mr avoids the issue:
> {code:java}
> set hive.cbo.enable=false;
> select a.id, b.name from a left outer join c on a.id = c.id left outer join b
> on a.id = b.id where b.name is not null;
> OK
> 1 a
> 2 b
> Time taken: 9.614 seconds, Fetched: 2 row(s)
> set hive.cbo.enable=true;
> set hive.execution.engine=mr;
> select a.id, b.name from a left outer join c on a.id = c.id left outer join b
> on a.id = b.id where b.name is not null;
> OK
> 1 a
> 2 b
> Time taken: 29.377 seconds, Fetched: 2 row(s)
> {code}
> Issue doesn't occur when using 'is null':
> {code:java}
> select a.id, b.name from a left outer join c on a.id = c.id left outer join b
> on a.id = b.id where b.name is null;
> OK
> 3 NULL
> Time taken: 9.673 seconds, Fetched: 1 row(s)
> {code}
> Explain plans for queries attached.
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