Thanks Dawid for bringing this ticket to dev mailing list and Timo’s kindly 
ping.

Firstly the example result is a little strange for me too, the print 
window_time looks incorrect, Could you post your entire example especially your 
session time zone?

Back to the window_start/end return type, both window TVF and legacy 
SqlGroupedWindowFunction share same return type TIMESTAMP which means timestamp 
literal, and it’s by design. We aims to address window correctness issue in DST 
timezone, there’re detailed explanation in CALCITE-4563.


Best,
Leonard

[1]https://issues.apache.org/jira/browse/CALCITE-4563



>> I wanted to bring your attention to FLINK-36665[1].
>> I believe the current behaviour is confusing and I'd like to fix it.
>> However, since window operations are a very important feature I'd like to
>> gather feedback on to what extent we should keep backwards compatibility.
>>    1. How should newly submitted queries behave? Are we fine with changing
>>    the inference of these functions or would you prefer to have a feature 
>> flag
>>    that would let us revert to the old inference logic? My preference would 
>> be
>>    to simply change the inference. The current behaviour is very confusing 
>> and
>>    I'd keep the behaviour for restored queries (see 2.)
>>    2. My plan for migrated queries (queries restored from a compiled plan)
>>    is that they won't be impacted. They'll keep producing the same results. 
>> We
>>    have the output types serialized in the compiled plan which we can use to
>>    produce the same type as before.
>> What do you think?
>> Best,
>> Dawid
>> [1] https://issues.apache.org/jira/browse/FLINK-36665
> 

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