Hello , Can someone help me in understanding Window join vs Window coGroup

When you use a window join, your join function will be applied for each match of the tuple (IN1_key, IN2_key). If there's no match (i.e. there are no elements IN1_key matching IN2_key), elements will not be emitted to your join function. However, the input for Cogroup is an iterable of IN_key1 and IN_key2, where each one of the iterables may be empty. This means that if IN1_key exists, but no matching IN2_key, the Cogroup function will still be invoked with an empty iterable for IN2_key. This generalization allows you to implement outer join semantics as well.

Thank you for the explanation. If this was the only difference, configuring window join with options like LEFT, RIGHT, INNER, and OUTER would have been better to understand the concepts. 🙂

You might want to take a look at the Table API & SQL where these operators are available. https://nightlies.apache.org/flink/flink-docs-master/docs/dev/table/tableapi/#outer-join

Sure. Thanks you so much