[jira] [Resolved] (HIVE-21575) Add support for SQL:2016 datetime templates/patterns/masks and CAST(... AS ... FORMAT )

["Karen Coppage (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-21575?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Karen Coppage resolved HIVE-21575.
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    Resolution: Done

> Add support for SQL:2016 datetime templates/patterns/masks and CAST(... AS ... FORMAT <pattern>)
> ------------------------------------------------------------------------------------------------
>
>                 Key: HIVE-21575
>                 URL: https://issues.apache.org/jira/browse/HIVE-21575
>             Project: Hive
>          Issue Type: Improvement
>            Reporter: Karen Coppage
>            Assignee: Karen Coppage
>            Priority: Major
>              Labels: SQL, datetime
>
> *Summary*
>  Timestamp and date handling and formatting is currently implemented in Hive using (sometimes very specific) [Java SimpleDateFormat patterns|http://docs.oracle.com/javase/8/docs/api/java/text/SimpleDateFormat.html] , however, it is not what most standard SQL systems use. For example see [Vertica|https://my.vertica.com/docs/7.2.x/HTML/Content/Authoring/SQLReferenceManual/Functions/Formatting/TemplatePatternsForDateTimeFormatting.htm], [Netezza|http://www.ibm.com/support/knowledgecenter/SSULQD_7.2.1/com.ibm.nz.dbu.doc/r_dbuser_ntz_sql_extns_templ_patterns_date_time_conv.html], [Oracle|https://docs.oracle.com/database/121/SQLRF/sql_elements004.htm#SQLRF00212], and [PostgreSQL|https://www.postgresql.org/docs/9.5/static/functions-formatting.html#FUNCTIONS-FORMATTING-DATETIME-TABLE].
> *Cast...Format*
> SQL:2016 also introduced the FORMAT clause for CAST which is the standard way to do string <-> datetime conversions
> For example:
> {code:java}
> CAST(<datetime> AS <char string type> [FORMAT <template>])
> CAST(<char string> AS <datetime type> [FORMAT <template>])
> cast(dt as string format 'DD-MM-YYYY')
> cast('01-05-2017' as date format 'DD-MM-YYYY')
> {code}
> [Stuff like this|http://bigdataprogrammers.com/string-date-conversion-hive/] wouldn't need to happen.
> *New SQL:2016 Patterns*
> Some conflicting examples:
> SimpleDateTime: 'MMM dd, yyyy HH:mm:ss'
>  SQL:2016: 'mon dd, yyyy hh24:mi:ss'
> SimpleDateTime: 'yyyy-MM-dd HH:mm:ss'
>  SQL:2016: 'yyyy-mm-dd hh24:mi:ss'
> For the full list of patterns, see subsection "Proposal for Impala’s datetime patterns" in this doc: [https://docs.google.com/document/d/1V7k6-lrPGW7_uhqM-FhKl3QsxwCRy69v2KIxPsGjc1k/edit]
> *Continued usage of SimpleDateFormat patterns*
> [Update] This feature will NOT be behind a flag in order to keep things simple for users. Existing Hive functions that accept SimpleDateFormat patterns as input will continue to do so. Please let me know if you disagree with this decision. These are the functions (afaik) affected:
>  * from_unixtime(bigint unixtime[, string format])
>  * unix_timestamp(string date, string pattern)
>  * to_unix_timestamp(date[, pattern])
>  * add_months(string start_date, int num_months, output_date_format)
>  * date_format(date/timestamp/string ts, string fmt)
> This description is a heavily edited description of IMPALA-4018.



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