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https://issues.apache.org/jira/browse/FLINK-18830?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17194313#comment-17194313
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liupengcheng commented on FLINK-18830:
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Hi, [~aljoscha] It's about both of them. I'm thinking about changing the
behaviour of the DataStream API and making outer join possible. Also, this can
be used in sql cases.
I'm now working on implementing window operations based on the window
table-valued function introduced by calcite-1.23+, the outer join can be
supported in this cases with this changes.
I'm also thinking about open an issue for introducing this window table-valued
function feature into flink. What do you think?
more details about window table-valued function, refer to these links:
https://docs.google.com/document/d/138uA7VTpbF84CFrd--cz3YVe0-AQ9ALnsavaSE2JeE4/edit#
https://issues.apache.org/jira/browse/CALCITE-3271
> JoinCoGroupFunction and FlatJoinCoGroupFunction work incorrectly for outer
> join when one side of coGroup is empty
> -----------------------------------------------------------------------------------------------------------------
>
> Key: FLINK-18830
> URL: https://issues.apache.org/jira/browse/FLINK-18830
> Project: Flink
> Issue Type: Bug
> Components: API / DataStream
> Affects Versions: 1.11.1
> Reporter: liupengcheng
> Priority: Major
>
> Currently, The {{JoinCoGroupFunction}} and {{FlatJoinCoGroupFunction}} in
> JoinedStreams doesn't respect the join type, it's been implemented as doing
> join within a two-level loop. However, this is incorrect for outer join when
> one side of the coGroup is empty.
> {code}
> public void coGroup(Iterable<T1> first, Iterable<T2> second,
> Collector<T> out) throws Exception {
> for (T1 val1: first) {
> for (T2 val2: second) {
> wrappedFunction.join(val1, val2, out);
> }
> }
> }
> {code}
> The above code is the current implementation, suppose the first input is
> non-empty, and the second input is an empty iterator, then the join
> function(`wrappedFunction`) will never be called. This will cause no data to
> be emitted for a left outer join.
> So I propose to consider join type here, and handle this case, e.g., for left
> outer join, we can emit record with right side set to null here if the right
> side is empty or can not find any match in the right side.
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