[jira] [Commented] (FLINK-3848) Add ProjectableTableSource interface and translation rule

["Fabian Hueske (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-3848?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15279989#comment-15279989 ] 

Fabian Hueske commented on FLINK-3848:
--------------------------------------

It turned out that the issue is more involved than I expected. 
Here is my current working branch: https://github.com/fhueske/flink/tree/tableProjectSource

[~dawidwys], I'll add some details about the challenges with this issue later. Need some time to look into it again.


> 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
>            Reporter: Fabian Hueske
>            Assignee: Fabian Hueske
>
> 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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