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https://issues.apache.org/jira/browse/FLINK-7755?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16209189#comment-16209189
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Fabian Hueske commented on FLINK-7755:
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I think we should treat this kind of bugs as blockers.
If something fails or doesn't work it is bad, but if it returns wrong results
without users noticing its much worse, IMO.
> 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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