Jackie-Jiang commented on issue #4740: [New Transformation function] Presto 
compatible DateTrunc
URL: https://github.com/apache/incubator-pinot/pull/4740#issuecomment-547159128
 
 
   @agrawaldevesh Thanks for the explanation. 
   IMO, `date_trunc()` should not have any knowledge of the timezone, but only 
truncate the time based on the given timestamp. Given the input value, 
`date_trunc()` should be able to figure out the input granularity 
automatically, and truncate it to the specified truncation interval. With 
these, we can achieve the standard `date_trunc()` semantic with only 2 
arguments, e.g. `date_trunc('DAYS', timestamp)`.
   Then the missing part is a timezone conversion function from arbitrary 
timezone & value to a timestamp in another timezone. The time value can be of 
numeric type or string type (e.g. DateTimeFormat).
   With these 2 functions de-coupled and chain-able, it becomes much more 
flexible. We can support timestamp/DateTimeFormat input in any timezone, and 
return truncated timestamp in another timezone. Also, we have the standard 
semantic for `date_trunc()` function.
   What do you think? Does this proposal meet all the requirements for the 
Presto connector?

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