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https://issues.apache.org/jira/browse/IMPALA-8386?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16811056#comment-16811056
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Quanlong Huang commented on IMPALA-8386:
----------------------------------------
Thank you, [~csringhofer]! (BTW, your query returns 2 but it should be 3)
I finally found out how the "amount = amount" predicate is generated. We
already have some logic to remove this kind of conjuncts but the existing
checks have exceptions which cause this bug.
Patch: https://gerrit.cloudera.org/c/12939/
> Incorrect predicate in a left outer join query
> ----------------------------------------------
>
> Key: IMPALA-8386
> URL: https://issues.apache.org/jira/browse/IMPALA-8386
> Project: IMPALA
> Issue Type: Bug
> Components: Frontend
> Reporter: Quanlong Huang
> Assignee: Quanlong Huang
> Priority: Critical
> Labels: correctness
>
> skyyws <[email protected]> reported a bug [in the mailing
> list|https://lists.apache.org/thread.html/0bdbbaa6bb35b552f050ae30587b7d75b78a72ec60007a8bc0a4a8a9@%3Cdev.impala.apache.org%3E]
> on the following data set:
> {code:java}
> table A
> +------+
> | a_id |
> +------+
> | 1 |
> | 2 |
> +------+
> table B
> +------+--------+
> | b_id | amount |
> +------+--------+
> | 1 | 10 |
> | 1 | 20 |
> | 2 | NULL |
> +------+--------+
> table C
> +------+------+
> | a_id | b_id |
> +------+------+
> | 1 | 1 |
> | 2 | 2 |
> +------+------+{code}
> The following query returns a wrong result "1":
> {code:java}
> select count(1) from (
> select t2.a_id,t2.amount1,t2.amount2
> from( select a_id from a) t1
> left outer join (
> select c.a_id,sum(amount) as amount1,sum(amount) as amount2
> from b join c on b.b_id = c.b_id group by c.a_id) t2
> on t1.a_id = t2.a_id
> ) t;
> {code}
> Removing "t2.amount2" can get the right result "2":
> {code:java}
> select count(1) from (
> select t2.a_id,t2.amount1
> from( select a_id from a) t1
> left outer join (
> select c.a_id,sum(amount) as amount1,sum(amount) as amount2
> from b join c on b.b_id = c.b_id group by c.a_id) t2
> on t1.a_id = t2.a_id
> ) t;
> {code}
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