Yongjun Zhang created IMPALA-8276:
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Summary: 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
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 is the same, 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 count(*) from (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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