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From "Kurt Young (JIRA)" <j...@apache.org>
Subject [jira] [Closed] (FLINK-11944) Support FirstRow and LastRow for SQL
Date Mon, 20 May 2019 01:26:00 GMT

     [ https://issues.apache.org/jira/browse/FLINK-11944?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Kurt Young closed FLINK-11944.
------------------------------
       Resolution: Duplicate
    Fix Version/s: 1.9.0

> Support FirstRow and LastRow for SQL
> ------------------------------------
>
>                 Key: FLINK-11944
>                 URL: https://issues.apache.org/jira/browse/FLINK-11944
>             Project: Flink
>          Issue Type: New Feature
>          Components: Table SQL / Runtime
>            Reporter: Jark Wu
>            Priority: Major
>             Fix For: 1.9.0
>
>
> Usually there are some duplicate data in the source due to some reasons.  In order to
get a correct result, we need to do deduplication. FirstRow and LastRow are two different
strategy for deduplication. The syntax of FirstRow and LastRow is similar to TopN, but order
by a time attribute. For example: 
> SELECT *
> FROM (
>   SELECT *, 
>   ROW_NUMBER() OVER (PARTITION BY id ORDER BY proctime DESC) as rownum
>   FROM T
> )
> WHERE rownum = 1
> Some information about FirstRow & LastRow.
> 1. the partition by key is the deduplicate key
> 2. can only order by a time attribute (either proctime or rowtime)
> 3. the rownum filter must be {{= 1}} or {{<= 1}}
> 4. it is FirstRow when order direction is ASC,  LastRow when order direction is DESC
> This issue is aiming to optimize this query to a FirstLastRow node instead of Over plus
Calc. And translate the it into physical operators.



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