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https://issues.apache.org/jira/browse/FLINK-7755?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16208992#comment-16208992
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Fabian Hueske commented on FLINK-7755:
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We compute wrong results. This is qualifies as a blocker, 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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