[GitHub] [arrow-rs] waitingkuo commented on issue #3664: Support UTF8 cast to Timestamp with timezone

["waitingkuo (via GitHub)" <gi...@apache.org>]

waitingkuo commented on issue #3664:
URL: https://github.com/apache/arrow-rs/issues/3664#issuecomment-1420335167

   > @tustvold sorry probably I have expressed not very clear. The entire idea is to cast user provided Utf8 value to Timestamp with timezone like
   > 
   > ```
   > select "2023-01-01 04:05:06.789-8"::timestamptz union all
   > select "2023-01-01 04:05:06.789-7"::timestamptz
   > ```
   > 
   > In Datafusion such transformation happens through arrow-rs `cast` function which has single target datatype , in this specific case I believe it would be `DataType::Timestamp(TimeUnit::Nanosecond, Something)` where is Something is not very clear for me. Presumably we can use `+00:00` or `None`, I'm struggling if we can lose precision in this case.
   
   I think casting to timestamptz should return the same time zone (the one shown in `SHOW TIME ZONE`) in the same query.
   
   i'm in UTC+8
   
   in postgresql, `select '2023-01-01 04:05:06.789-8'::timestamptz` returns timestamptz in UTC+8
   ```bash
   willy=# select '2023-01-01T04:05:06.789-8'::timestamptz;
           timestamptz         
   ----------------------------
    2023-01-01 20:05:06.789+08
   (1 row)
   ```
   
   ```bash
   willy=# select '2023-01-01 04:05:06.789-7'::timestamptz;
           timestamptz         
   ----------------------------
    2023-01-01 19:05:06.789+08
   (1 row)
   ```
   
   so in your query, the union return +8 time zone (my current time zone) for me in postgresql.
   
   I think we could consider either fix it to +00:00 or  current timezone 
   
   
   
   


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