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https://issues.apache.org/jira/browse/FLINK-3848?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15725773#comment-15725773
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ASF GitHub Bot commented on FLINK-3848:
---------------------------------------

Github user fhueske commented on a diff in the pull request:

    https://github.com/apache/flink/pull/2810#discussion_r91078799
  
    --- Diff: 
flink-libraries/flink-table/src/test/scala/org/apache/flink/api/scala/stream/ExplainStreamTest.scala
 ---
    @@ -19,7 +19,9 @@
     package org.apache.flink.api.scala.stream
     
     import org.apache.flink.api.scala._
    +import org.apache.flink.api.scala.stream.utils.StreamTestData
    --- End diff --
    
    Remove imports


> Add ProjectableTableSource interface and translation rule
> ---------------------------------------------------------
>
>                 Key: FLINK-3848
>                 URL: https://issues.apache.org/jira/browse/FLINK-3848
>             Project: Flink
>          Issue Type: New Feature
>          Components: Table API & SQL
>            Reporter: Fabian Hueske
>            Assignee: Anton Solovev
>
> Add a {{ProjectableTableSource}} interface for {{TableSource}} implementation 
> that support projection push-down.
> The interface could look as follows
> {code}
> def trait ProjectableTableSource {
>   def setProjection(fields: Array[String]): Unit
> }
> {code}
> In addition we need Calcite rules to push a projection into a TableScan that 
> refers to a {{ProjectableTableSource}}. We might need to tweak the cost model 
> as well to push the optimizer in the right direction.
> Moreover, the {{CsvTableSource}} could be extended to implement 
> {{ProjectableTableSource}}.



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