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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-6465) support FIRST_VALUE on Table API & SQL
Date Thu, 17 Aug 2017 03:13:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-6465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16129822#comment-16129822
] 

ASF GitHub Bot commented on FLINK-6465:
---------------------------------------

GitHub user sunjincheng121 opened a pull request:

    https://github.com/apache/flink/pull/4556

    [FLINK-6465][table]support FIRST_VALUE on Table API & SQL

    *Thank you very much for contributing to Apache Flink - we are happy that you want to
help us improve Flink. To help the community review your contribution in the best possible
way, please go through the checklist below, which will get the contribution into a shape in
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    ## Contribution Checklist
    
      - Make sure that the pull request corresponds to a [JIRA issue](https://issues.apache.org/jira/projects/FLINK/issues).
Exceptions are made for typos in JavaDoc or documentation files, which need no JIRA issue.
      
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where *FLINK-XXXX* should be replaced by the actual issue number. Skip *component* if you
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      Typo fixes that have no associated JIRA issue should be named following this pattern:
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for PuncuatedWatermarkGenerator`.
    
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    **(The sections below can be removed for hotfixes of typos)**
    
    ## What is the purpose of the change
    This PR. try to add `FIRST_VALUE` aggregate function OVER window on table API&SQL.
    
    ## Brief change log
    - *Add `FIRST_VALUE` aggregate function.
    - *Add `FIRST_VALUE` test in OVER window.
    - *Add `FIRST_VALUE` test case.(only for aggregate function)
    
    ## Verifying this change
    This change added tests and can be verified as follows:
      - *Added integration tests for over window(tableAPI&SQL)
      - *Added test that validates that  `FIRST_VALUE` can deal with BYTE/SHORT/INT/LONG/DOUBLE/STRING/BIGDECIMAL
      
    ## Does this pull request potentially affect one of the following parts:
    
      - Dependencies (does it add or upgrade a dependency): (no)
      - The public API, i.e., is any changed class annotated with `@Public(Evolving)`: ( no)
      - The serializers: (no)
      - The runtime per-record code paths (performance sensitive): (no)
      - Anything that affects deployment or recovery: JobManager (and its components), Checkpointing,
Yarn/Mesos, ZooKeeper: (no)
    
    ## Documentation
    
      - Does this pull request introduce a new feature? (yes)
      - If yes, how is the feature documented? (docs)
    


You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/sunjincheng121/flink FLINK-6465-PR

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/flink/pull/4556.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #4556
    
----
commit b6278aa3a318ba647dfa6aa96790dd18131a7670
Author: sunjincheng121 <sunjincheng121@gmail.com>
Date:   2017-08-17T02:56:50Z

    [FLINK-6465][table]support FIRST_VALUE on Table API & SQL

----


> support FIRST_VALUE on Table API & SQL
> --------------------------------------
>
>                 Key: FLINK-6465
>                 URL: https://issues.apache.org/jira/browse/FLINK-6465
>             Project: Flink
>          Issue Type: New Feature
>          Components: Table API & SQL
>            Reporter: Hequn Cheng
>            Assignee: sunjincheng
>
> {{FIRST_VALUE}} is a OVER WINDOW function. In this JIRA. will add {{FIRST_VALUE}} function
support on TableAPI & SQL.
> *Syntax:*
> FIRST_VALUE ( [scalar_expression ] )   
>     OVER ( [ partition_by_clause ] order_by_clause [ rows_range_clause ] )  [About OVER
WINDOWS|https://ci.apache.org/projects/flink/flink-docs-release-1.4/dev/table/tableApi.html#over-windows]
> scalar_expression
> Is the value to be returned. scalar_expression can be a column, or other arbitrary expression
that results in a single value. Other analytic functions are not permitted.
> *NOTE:*
> *  {{FIRST_VALUE}} if used for OVER WINDOW, e.g.: 
> {code}
> SELECT A, B, FIRST_VALUE(C) OVER (ORDER BY E) AS firstValue FROM tab
> {code}
> * OVER WINDOW's retraction is expensive(currently not supported yet), and this JIRA.
does not implement Retract logic of {{FIRST_VALUE}}.



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