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From "Till Rohrmann (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-7755) Null values are not correctly handled by batch inner and outer joins
Date Wed, 18 Oct 2017 11:41:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-7755?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16209183#comment-16209183
] 

Till Rohrmann commented on FLINK-7755:
--------------------------------------

But this bug is already present since Flink 1.3, right? I wouldn't really block 1.4 on this
issue. Even though I think we should try to push hard to get it in for 1.4.

> Null values are not correctly handled by batch inner and outer joins
> --------------------------------------------------------------------
>
>                 Key: FLINK-7755
>                 URL: https://issues.apache.org/jira/browse/FLINK-7755
>             Project: Flink
>          Issue Type: Bug
>          Components: Table API & SQL
>    Affects Versions: 1.4.0, 1.3.2
>            Reporter: Fabian Hueske
>            Assignee: Fabian Hueske
>            Priority: Blocker
>             Fix For: 1.4.0, 1.3.3
>
>
> Join predicates of batch joins are not correctly evaluated according to three-value logic.
> This affects inner as well as outer joins.
> The problem is that some equality predicates are only evaluated by the internal join
algorithms of Flink which are based on {{TypeComparator}}. The field {{TypeComparator}} for
{{Row}} are implemented such that {{null == null}} results in {{TRUE}} to ensure correct ordering
and grouping. However, three-value logic requires that {{null == null}} results to {{UNKNOWN}}
(or null). The code generator implements this logic correctly, but for equality predicates,
no code is generated.
> For outer joins, the problem is a bit tricker because these do not support code-generated
predicates yet (see FLINK-5520). FLINK-5498 proposes a solution for this issue.
> We also need to extend several of the existing tests and add null values to ensure that
the join logic is correctly implemented. 



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