[
https://issues.apache.org/jira/browse/FLINK-18830?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Dawid Wysakowicz updated FLINK-18830:
-------------------------------------
Description:
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.
was:
Currently, The `JoinCoGroupFunction` and `FlatJoinCoGroupFunction` in
JoinedStreams does'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.
```
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);
}
}
}
```
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.
> 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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