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https://issues.apache.org/jira/browse/HIVE-27673?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17765527#comment-17765527
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Stamatis Zampetakis commented on HIVE-27673:
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I updated the wiki to reflect the changes in date_format and
hive.datetime.formatter property:
* https://cwiki.apache.org/confluence/display/Hive/LanguageManual+UDF
*
https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties#ConfigurationProperties-Datetime
> 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
> Priority: Major
> Labels: pull-request-available
> Fix For: 4.0.0
>
>
> 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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