Stamatis Zampetakis created HIVE-27673:
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Summary: Configurable datetime formatter for date_format
Key: HIVE-27673
URL: https://issues.apache.org/jira/browse/HIVE-27673
Project: Hive
Issue Type: Improvement
Components: HiveServer2
Affects Versions: 4.0.0-beta-1
Reporter: Stamatis Zampetakis
Assignee: Stamatis Zampetakis
HIVE-25268 switched the internal implementation of date_format from
java.text.SimpleDateFormat to java.time.format.DateTimeFormatter in order to
avoid some inconsistencies (arguably wrong results) for dates prior to 1900.
However, the API of the underlying formatter is exposed to the user since they
need to pass patterns that are valid for the respective formatter.
Changing the formatter implementation resolves the bugs in HIVE-25268 but also
leads to backward incompatible behavior.
Consider for example the following query where the letter 'u' is used to format
the date:
{code:sql}
select date_format('2023-09-08','u');
{code}
The query above will return different result depending on the formatter that is
used underneath.
In
[SimpleDateFormat|https://docs.oracle.com/javase/8/docs/api/java/text/SimpleDateFormat.html],
the letter 'u' means day of the week so the query returns 5.
In
[DateTimeFormatter|https://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html],
the letter 'u' means year so the query returns 2023.
The goal of this ticket is to make the underlying formatter of date_format
function configurable by the end-user via property, similarly to what was done
in HIVE-25576. For this purpose we could reuse the same property:
hive.datetime.formatter
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