Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/3715#discussion_r125482464
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/plan/nodes/datastream/DataStreamWindowJoin.scala
---
@@ -87,44 +98,38 @@ class DataStreamRowStreamJoin(
val config = tableEnv.getConfig
+ val leftIsAccRetract = DataStreamRetractionRules.isAccRetract(left)
--- End diff --
Retractions are just one (of two) ways to encode updates in a stream. This
join implementation does not support any kind of updates (which is fine).
However, we have to check if the input streams produce updates or not. The
`StreamTableEnvironment` has a private class `AppendOnlyValidator`. We should
move `AppendOnlyValidator` and `UniqueKeyExtractor` into a class `UpdateUtils`
together with the methods `isAppendOnly()` and `getUniqueKeyFields()`.
`isAppendOnly()` checks if an operator produces updates or not and should be
used here.
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