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https://issues.apache.org/jira/browse/FLINK-7730?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16205157#comment-16205157
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Fabian Hueske commented on FLINK-7730:
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This is mainly problem in Calcite (see [this thread on the Calcite dev
list|https://lists.apache.org/thread.html/16caeb8b1649c4da85f9915ea723c6c5b3ced0b96914cadc24ee4e15@%3Cdev.calcite.apache.org%3E])
Seems like there is no easy fix to solve this issue. We might want to check if
we can forbid predicates in the {{ON}} clause of an {{OUTER JOIN}} against a
{{LATERAL TABLE}}. This would probably involve copying and modifying Calcite
code until the issue is fixed in a newer Calcite release.
> TableFunction LEFT OUTER joins with ON predicates are broken
> ------------------------------------------------------------
>
> Key: FLINK-7730
> URL: https://issues.apache.org/jira/browse/FLINK-7730
> Project: Flink
> Issue Type: Bug
> Components: Table API & SQL
> Affects Versions: 1.4.0, 1.3.2
> Reporter: Fabian Hueske
> Assignee: Xingcan Cui
>
> TableFunction left outer joins with predicates in the ON clause are broken.
> Apparently, the are no tests for this and it has never worked. I observed
> issues on several layers:
> - Table Function does not correctly validate equality predicate:
> {{leftOuterJoin(func1('c) as 'd, 'a.cast(Types.STRING) === 'd)}} is rejected
> because the predicate is not considered as an equality predicate (the cast
> needs to be pushed down).
> - Plans cannot be correctly translated: {{leftOuterJoin(func1('c) as 'd, 'c
> === 'd)}} gives an optimizer exception.
> - SQL queries get translated but produce incorrect results. For example
> {{SELECT a, b, c, d FROM MyTable LEFT OUTER JOIN LATERAL TABLE(tfunc(c)) AS
> T(d) ON d = c}} returns an empty result if the condition {{d = c}} never
> returns true. However, the outer side should be preserved and padded with
> nulls.
> So there seem to be many issues with table function outer joins. Especially,
> the wrong result produced by SQL queries need to be quickly fixed.
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