I actually managed to fixed this already :) For those wondering, I grouped by 
both window start and end first. That did it!

> On 19. Dec 2022, at 15:43, Theodor Wübker <theo.wueb...@inside-m2m.de> wrote:
> 
> Hey everyone,
> 
> I would like to run a Windowing-SQL query with a group-by clause on a Kafka 
> topic and write the result back to Kafka. Right now, the program always says 
> that I am creating an update-stream that can only be written to an 
> Upsert-Kafka-Sink. That seems odd to me, because running my grouping over a 
> tumbling window should only require writing the result to kafka exactly once. 
> Quote from docs [1]: 'Unlike other aggregations on continuous tables, window 
> aggregation do not emit intermediate results but only a final result, the 
> total aggregation at the end of the window'
> I understand that ‘group-by’ should generate an update-stream as long as 
> there is no windowing happening - but there is in my case. How can I get my 
> program to not create an update-, but a simple append stream instead? My 
> query looks roughly like this:
> 
> "SELECT x, window_start, count(*) as y 
> FROM TABLE(TUMBLE(TABLE my_table, DESCRIPTOR(timestamp), INTERVAL '1' DAY))
> GROUP BY x, window_start”
> 
> -Theo
> 
> 
> [1] 
> https://nightlies.apache.org/flink/flink-docs-master/docs/dev/table/sql/queries/window-agg/
>  
> <https://nightlies.apache.org/flink/flink-docs-master/docs/dev/table/sql/queries/window-agg/>

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