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https://issues.apache.org/jira/browse/IMPALA-7957?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16820628#comment-16820628
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Quanlong Huang commented on IMPALA-7957:
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Hi [~Paul.Rogers], I have a patch for this for review:
[https://gerrit.cloudera.org/c/13051]
Could you have a look when you have time?
> UNION ALL query returns incorrect results
> -----------------------------------------
>
> Key: IMPALA-7957
> URL: https://issues.apache.org/jira/browse/IMPALA-7957
> Project: IMPALA
> Issue Type: Bug
> Components: Frontend
> Affects Versions: Impala 2.12.0
> Reporter: Luis E Martinez-Poblete
> Assignee: Paul Rogers
> Priority: Blocker
> Labels: correctness
>
> Synopsis:
> =========
> UNION ALL query returns incorrect results
> Problem:
> ========
> Customer reported a UNION ALL query returning incorrect results. The UNION
> ALL query has 2 legs, but Impala is only returning information from one leg.
> Issue can be reproduced in the latest version of Impala. Below is the
> reproduction case:
> {noformat}
> create table mytest_t (c1 timestamp, c2 timestamp, c3 int, c4 int);
> insert into mytest_t values (now(), ADDDATE (now(),1), 1,1);
> insert into mytest_t values (now(), ADDDATE (now(),1), 2,2);
> insert into mytest_t values (now(), ADDDATE (now(),1), 3,3);
> SELECT t.c1
> FROM
> (SELECT c1, c2
> FROM mytest_t) t
> LEFT JOIN
> (SELECT c1, c2
> FROM mytest_t
> WHERE c2 = c1) t2 ON (t.c2 = t2.c2)
> UNION ALL
> VALUES (NULL)
> {noformat}
> The above query produces the following execution plan:
> {noformat}
> +------------------------------------------------------------------------------------+
> | Explain String
> |
> +------------------------------------------------------------------------------------+
> | Max Per-Host Resource Reservation: Memory=34.02MB Threads=5
> |
> | Per-Host Resource Estimates: Memory=2.06GB
> |
> | WARNING: The following tables are missing relevant table and/or column
> statistics. |
> | default.mytest_t
> |
> |
> |
> | PLAN-ROOT SINK
> |
> | |
> |
> | 06:EXCHANGE [UNPARTITIONED]
> |
> | |
> |
> | 00:UNION
> |
> | | constant-operands=1
> |
> | |
> |
> | 04:SELECT
> |
> | | predicates: default.mytest_t.c1 = default.mytest_t.c2
> |
> | |
> |
> | 03:HASH JOIN [LEFT OUTER JOIN, BROADCAST]
> |
> | | hash predicates: c2 = c2
> |
> | |
> |
> | |--05:EXCHANGE [BROADCAST]
> |
> | | |
> |
> | | 02:SCAN HDFS [default.mytest_t]
> |
> | | partitions=1/1 files=3 size=192B
> |
> | | predicates: c2 = c1
> |
> | |
> |
> | 01:SCAN HDFS [default.mytest_t]
> |
> | partitions=1/1 files=3 size=192B
> |
> +------------------------------------------------------------------------------------+
> {noformat}
> The issue is in operator 4:
> {noformat}
> | 04:SELECT |
> | | predicates: default.mytest_t.c1 = default.mytest_t.c2 |
> {noformat}
> It's definitely a bug with predicate placement - that c1 = c2 predicate
> shouldn't be evaluated outside the right branch of the LEFT JOIN.
> Thanks,
> Luis Martinez.
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