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https://issues.apache.org/jira/browse/HIVE-3464?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13615729#comment-13615729
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Phabricator commented on HIVE-3464:
-----------------------------------
vikram has commented on the revision "HIVE-3464 [jira] Merging join tree may
reorder joins which could be invalid".
Question with regard to a new api introduced in the patch.
INLINE COMMENTS
ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java:6644 Could
you explain the use of the left variable in the api? The only use always seems
to set it to true and this variable is not used within the api itself.
REVISION DETAIL
https://reviews.facebook.net/D5409
To: JIRA, navis
Cc: njain, vikram
> 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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