This is a Breaking change when using window functions inside partition operator sub-query scope.
Window functions require a serialized/ordered input.
There is a bug in Azure Data Explorer logic that allows using window functions inside the partition operator when the ordering is performed outside the partition query scope like this:
| where Timestamp > ago(1d)
| order by Timestamp asc
| partition by key
extend next_value = next(value)
This kind of query currently works unintentionally and sometimes the output is not correct.
We’re planning to make a change that will fail this kind of queries by throwing a semantic error indicating that the input to the window function is not serialized.
Fix all relevant queries by pushing the ordering inside the partition subquery like shown below.
order by Timestamp asc
| extend next_value = next(value)
Support for previous window function pattern will be blocked - ETA: November 30, 2022
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