[GitHub] [arrow-datafusion] alamb commented on issue #686: Specific timezone support for `to_timetamp*()`

[GitBox <gi...@apache.org>]

alamb commented on issue #686:
URL: https://github.com/apache/arrow-datafusion/issues/686#issuecomment-874907741


   @velvia 
   
   > we have been using the output of None timestamps from DataFusion but we treat all our timestamps as UTC internally.
   
   FWIW this is what we do in IOx as well
   
   > The best solution I can think of would be for to_timestamp(...) to support a second, optional argument where the timezone can be specified. 
   
   I think a second optional argument for `to_timestamp` is a fine solution that would be backwards compatible and also allow for improvements going forward
   
   > For example, if I have data with a timezone of Some("UTC") the following fails due to incompatible types: WHERE timestamp_col > to_timestamp("2021-06-21T12:00Z") (because timestamp_col has Some(UTC) but to_timestamp returns None)
   
   I think a better solution would be for DataFusion to implement coercion rules between date/time/timestamp types. In your example of a timestamp_col with `Timestamp(Milliseconds, Some("UTC")`), then I would *like* DataFusion to handle
   
   ```
   WHERE timestamp_col > to_timestamp("2021-06-21T12:00Z")
   ```
   
   by adding the following cast (please forgive me the pseudo-SQL)
   
   ```
   WHERE timestamp_col > cast (to_timestamp("2021-06-21T12:00Z") as timestamp(UTC))
   ```
   
   


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