Github user hequn8128 commented on a diff in the pull request:
https://github.com/apache/flink/pull/5327#discussion_r184993658
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/plan/nodes/datastream/DataStreamJoin.scala
---
@@ -60,6 +60,9 @@ class DataStreamJoin(
override def needsUpdatesAsRetraction: Boolean = true
+ // outer join will generate retractions
+ override def producesRetractions: Boolean = joinType != JoinRelType.INNER
--- End diff --
Inner join doesn't produce retractions, left/right/full join does, for
example, left join will retract the previous non-matched output when new
matched row comes from the right side.
---
