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Pay attention, that both streams are use as examples for KStream (ie, record stream) and KTable (ie, changelog stream) with different semantics. For KTable, so-called tombstone records with format key:null are of special interest, as they delete a key (those records are shown as null in all examples to highlight tombstone semantics). Last but not least, in Kafka Streams each join is "customized" by the user with a ValueJoiner function that compute the actual result. Hence, we show output records as "X - Y" with X and Y being the left and right value, respectively, given to the value joiner. If the output is shown as null (ie, tombstone message), ValueJoiner will not be called because a result record will be deleted.

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spurious spurious

Improved Left/Outer Stream-Stream Join (v3.0.x and newer)

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Warning
Prior to version 3.0.x Kafka Streams might emit so called "spurious" left/outer join result. In this section we only explain the different new behavior that avoids spurious left/outer stream-stream join results. See New Join Semantics below that describe all joins in more details, including spurious left/output join behavior in versions 0.10.2.x  to 2.8.x.

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