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https://issues.apache.org/jira/browse/HIVE-8225?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14162802#comment-14162802
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Pengcheng Xiong commented on HIVE-8225:
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[~sershe], I have just tried select unionsrc.key FROM (select 'tst1' as key,
count(1) as value from src s1) unionsrc;
the output is "tst1" as we expect.
> CBO trunk merge: union11 test fails due to incorrect plan
> ---------------------------------------------------------
>
> Key: HIVE-8225
> URL: https://issues.apache.org/jira/browse/HIVE-8225
> Project: Hive
> Issue Type: Bug
> Reporter: Sergey Shelukhin
> Assignee: Sergey Shelukhin
> Priority: Critical
> Fix For: 0.14.0
>
> Attachments: HIVE-8225.1.patch, HIVE-8225.2.patch, HIVE-8225.3.patch,
> HIVE-8225.4.patch, HIVE-8225.5.patch, HIVE-8225.inprogress.patch,
> HIVE-8225.inprogress.patch, HIVE-8225.patch
>
>
> The result changes to as if the union didn't have count() inside. The issue
> can be fixed by using srcunion.value outside the subquery in count (replace
> count(1) with count(srcunion.value)). Otherwise, it looks like count(1) node
> from union-ed queries is not present in AST at all, which might cause this
> result.
> -Interestingly, adding group by to each query in a union produces completely
> weird result (count(1) is 309 for each key, whereas it should be 1 and the
> "logical" incorrect value if internal count is lost is 500)- Nm, that groups
> by table column called key, which is weird but is what Hive does
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