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Posted to issues@flink.apache.org by "luoyuxia (Jira)" <ji...@apache.org> on 2022/06/09 03:19:00 UTC
[jira] [Commented] (FLINK-26764) Support RESPECT NULLS for FIRST_VALUE/LAST_VALUE
[ https://issues.apache.org/jira/browse/FLINK-26764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17551924#comment-17551924 ]
luoyuxia commented on FLINK-26764:
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When I try to support it, I meet some problem. Currently, in Flink, the FIRST_VALUE always ignore null by default. But in almost all other engine like [Spark|https://spark.apache.org/docs/2.4.2/api/sql/index.html#first_value], [Hive|https://cwiki.apache.org/confluence/display/hive/languagemanual+windowingandanalytics], [Oracle|https://docs.oracle.com/cd/B19306_01/server.102/b14200/functions057.htm], [Snowflake|https://docs.snowflake.com/en/sql-reference/functions/first_value.html], etc always not ignore null by default.
In this case, we have two options:
1: Not to follow other engines' behavior. It's fine but may be not friendly to the other engines' users when they switch to Flink. Users may make mistake in this function.
2: Follow other engines' behavior. It make the behavior compatible with other engines, and thus more user friendly. But it will change the default behavior for FIRST_VALUE and will bring compatibility issue when user upgrade their Flink.
I'm fine with any one of these two options, but perfer the second one.
[~jark] [~godfreyhe] Could you please have a look?
> Support RESPECT NULLS for FIRST_VALUE/LAST_VALUE
> -------------------------------------------------
>
> Key: FLINK-26764
> URL: https://issues.apache.org/jira/browse/FLINK-26764
> Project: Flink
> Issue Type: New Feature
> Components: Table SQL / API, Table SQL / Planner
> Reporter: luoyuxia
> Assignee: luoyuxia
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.16.0
>
>
> Flink supports fucntion FIRST_VALUE/LAST_VALUE, but the behavior is always ignore null value.
> But the [Spark|https://spark.apache.org/docs/2.4.2/api/sql/index.html#first_value], [Hive|https://cwiki.apache.org/confluence/display/hive/languagemanual+windowingandanalytics], [Oracle|https://docs.oracle.com/cd/B19306_01/server.102/b14200/functions057.htm], [Snowflake|https://docs.snowflake.com/en/sql-reference/functions/first_value.html], etc, also support to respect null for FIRST_VALUE/LAST_VALUE.
> Should we also support to allow users to specifc whether to ignore null?
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