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https://issues.apache.org/jira/browse/IMPALA-4018?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16756604#comment-16756604
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Greg Rahn commented on IMPALA-4018:
-----------------------------------
I'm not sure these can be split into two as the SQL patterns and Java patterns
have some conflicts and mean different things. My thoughts on introducing this
new syntax is that it would only work with the SQL patterns be ISO/ANSI SQL
compliant from the beginning. Thoughts [~Paul.Rogers]?
I'd say the numeric parts would be the most frequently used, the ones that make
up (yyyy-mm-dd hh24:mi:ss.ff9)
> Add support for SQL:2016 datetime templates/patterns/masks to CAST(... AS ...
> FORMAT <template>)
> ------------------------------------------------------------------------------------------------
>
> Key: IMPALA-4018
> URL: https://issues.apache.org/jira/browse/IMPALA-4018
> Project: IMPALA
> Issue Type: New Feature
> Components: Frontend
> Affects Versions: Impala 2.2.4
> Reporter: Greg Rahn
> Assignee: Gabor Kaszab
> Priority: Critical
> Labels: ansi-sql, compatibility, sql-language
>
> *Summary*
> The format masks/templates for currently are implemented using the [Java
> SimpleDateFormat
> patterns|http://docs.oracle.com/javase/8/docs/api/java/text/SimpleDateFormat.html],
> and although this is what Hive has implemented, it is not what most standard
> SQL systems implement. 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].
>
> *Examples of incompatibilities*
> {noformat}
> -- PostgreSQL/Netezza/Vertica/Oracle
> select to_timestamp('May 15, 2015 12:00:00', 'mon dd, yyyy hh:mi:ss');
> -- Impala
> select to_timestamp('May 15, 2015 12:00:00', 'MMM dd, yyyy HH:mm:ss');
> -- PostgreSQL/Netezza/Vertica/Oracle
> select to_timestamp('2015-02-14 20:19:07','yyyy-mm-dd hh24:mi:ss');
> -- Impala
> select to_timestamp('2015-02-14 20:19:07','yyyy-MM-dd HH:mm:ss');
> -- Vertica/Oracle
> select to_timestamp('2015-02-14 20:19:07.123456','yyyy-mm-dd hh24:mi:ss.ff');
> -- Impala
> select to_timestamp('2015-02-14 20:19:07.123456','yyyy-MM-dd
> HH:mm:ss.SSSSSS');
> {noformat}
> *Considerations*
> Because this is a change in default behavior for to_timestamp(), if possible,
> having a feature flag to revert to the legacy Java SimpleDateFormat patterns
> should be strongly considered. This would allow users to chose the behavior
> they desire and scope it to a session if need be.
> SQL:2016 defines the following datetime templates
> {noformat}
> <datetime template> ::=
> { <datetime template part> }...
> <datetime template part> ::=
> <datetime template field>
> | <datetime template delimiter>
> <datetime template field> ::=
> <datetime template year>
> | <datetime template rounded year>
> | <datetime template month>
> | <datetime template day of month>
> | <datetime template day of year>
> | <datetime template 12-hour>
> | <datetime template 24-hour>
> | <datetime template minute>
> | <datetime template second of minute>
> | <datetime template second of day>
> | <datetime template fraction>
> | <datetime template am/pm>
> | <datetime template time zone hour>
> | <datetime template time zone minute>
> <datetime template delimiter> ::=
> <minus sign>
> | <period>
> | <solidus>
> | <comma>
> | <apostrophe>
> | <semicolon>
> | <colon>
> | <space>
> <datetime template year> ::=
> YYYY | YYY | YY | Y
> <datetime template rounded year> ::=
> RRRR | RR
> <datetime template month> ::=
> MM
> <datetime template day of month> ::=
> DD
> <datetime template day of year> ::=
> DDD
> <datetime template 12-hour> ::=
> HH | HH12
> <datetime template 24-hour> ::=
> HH24
> <datetime template minute> ::=
> MI
> <datetime template second of minute> ::=
> SS
> <datetime template second of day> ::=
> SSSSS
> <datetime template fraction> ::=
> FF1 | FF2 | FF3 | FF4 | FF5 | FF6 | FF7 | FF8 | FF9
> <datetime template am/pm> ::=
> A.M. | P.M.
> <datetime template time zone hour> ::=
> TZH
> <datetime template time zone minute> ::=
> TZM
> {noformat}
> SQL:2016 also introduced the FORMAT clause for CAST which is the standard way
> to do string <> datetime conversions
> {noformat}
> <cast specification> ::=
> CAST <left paren>
> <cast operand> AS <cast target>
> [ FORMAT <cast template> ]
> <right paren>
> <cast operand> ::=
> <value expression>
> | <implicitly typed value specification>
> <cast target> ::=
> <domain name>
> | <data type>
> <cast template> ::=
> <character string literal>
> {noformat}
> For example:
> {noformat}
> 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')
> {noformat}
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