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https://issues.apache.org/jira/browse/HIVE-3464?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13615730#comment-13615730
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Vikram Dixit K commented on HIVE-3464:
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[~navis] I went through the tests and code and I see how this affects the plan.
Could you please add tests that produce some output rows. You could add
something like
{noformat}
insert overwrite table a select * from src;
{noformat}
in your test file(mergejoins_mixed.q). I see that when I remove the explain
statements associated with this test, a complicated query - inner, right outer
(different key), full outer is what produces a different output. Others seem
fine perhaps lucky.
Also had a comment on code review.
> Merging join tree may reorder joins which could be invalid
> ----------------------------------------------------------
>
> Key: HIVE-3464
> URL: https://issues.apache.org/jira/browse/HIVE-3464
> Project: Hive
> Issue Type: Bug
> Components: Query Processor
> Affects Versions: 0.10.0
> Reporter: Navis
> Assignee: Navis
> Attachments: HIVE-3464.D5409.2.patch, HIVE-3464.D5409.3.patch,
> HIVE-3464.D5409.4.patch
>
>
> Currently, hive merges join tree from right to left regardless of join types,
> which may introduce join reordering. For example,
> select * from a join a b on a.key=b.key join a c on b.key=c.key join a d on
> a.key=d.key;
> Hive tries to merge join tree in a-d=b-d, a-d=a-b, b-c=a-b order and a-d=a-b
> and b-c=a-b will be merged. Final join tree is "a-(bdc)".
> With this, ab-d join will be executed prior to ab-c. But if join type of -c
> and -d is different, this is not valid.
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