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https://issues.apache.org/jira/browse/IMPALA-8276?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tim Armstrong resolved IMPALA-8276.
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Resolution: Fixed
I'm going to call this a duplicate. I am 95% sure it's the same thing, but we
don't have the info here to reproduce and confirm, so it would be "cannot
reproduce" otherwise.
> Self equal to self predicate "x = x" generated by Impala caused incorrect
> query result
> --------------------------------------------------------------------------------------
>
> Key: IMPALA-8276
> URL: https://issues.apache.org/jira/browse/IMPALA-8276
> Project: IMPALA
> Issue Type: Bug
> Components: Frontend
> Affects Versions: Impala 3.0
> Reporter: Yongjun Zhang
> Priority: Blocker
> Labels: correctness
>
> Reported with cdh5.12.1, that "self equal to self" kind of bogus predicate "x
> = x" is generated by Impala and caused incorrect query result, because this
> kind of predicate return false for "null" entries.
> It was observed that a {{count(*)}} query returned fewer rows than a CTAS
> query, though the query body is the same for both, because the former
> generated the bogus predicate and the latter doesn't.
> For example,
> {code:java}
> select count(*) from
> (select a.*, b.x, b.y, b.z_dt, from view1 a left join view2 b on a.p = b.q)
> a{code}
> returned fewer rows than
> {code:java}
> create table abc as
> select a.*, b.x, b.y, b.z_dt, from view1 a left join view2 b on a.p =
> b.q{code}
> because predicate {{a.z = a.z_dt}} was created (for reasons to understand,
> notice b.z_dt is an alias of b.z), exhibited as "table1.z = table1.z" in the
> query plan in Impala query profile because a and b are aliases of view1 and
> view2, both of which are views created in a very nested way that involves
> table table1.
> Though in cdh5.12.1 the select and the count query returns different result
> in the initial case, an attempted reproduction shows that both queries get
> bogus predicates. And cdh5.15.2 has the same problem. Was not able to try
> out with most recent master branch of impala due to meta data incompatibility.
>
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