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https://issues.apache.org/jira/browse/FLINK-5698?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15871864#comment-15871864
 ] 

ASF GitHub Bot commented on FLINK-5698:
---------------------------------------

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

    https://github.com/apache/flink/pull/3269#discussion_r101755176
  
    --- Diff: 
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/plan/rules/util/RexProgramProjectExtractor.scala
 ---
    @@ -84,6 +105,39 @@ object RexProgramProjectExtractor {
     }
     
     /**
    +  * A RexVisitor to extract used nested input fields
    +  */
    +class RefFieldAccessorVisitor(
    +    usedFields: Array[Int],
    +    names: List[String])
    +  extends RexVisitorImpl[Unit](true) {
    +
    +  private val group = usedFields.toList
    +  private var nestedFields = mutable.LinkedHashSet[String]()
    +
    +  def getNestedFields: Array[String] = nestedFields.toArray
    +
    +  override def visitFieldAccess(fieldAccess: RexFieldAccess): Unit = {
    +    fieldAccess.getReferenceExpr match {
    +      case ref: RexInputRef =>
    +        nestedFields += 
s"${names(ref.getIndex)}.${fieldAccess.getField.getName}"
    --- End diff --
    
    I think it would be nice, if we would go deeper than just one level.


> Add NestedFieldsProjectableTableSource interface
> ------------------------------------------------
>
>                 Key: FLINK-5698
>                 URL: https://issues.apache.org/jira/browse/FLINK-5698
>             Project: Flink
>          Issue Type: New Feature
>          Components: Table API & SQL
>            Reporter: Anton Solovev
>            Assignee: Anton Solovev
>
> Add a NestedFieldsProjectableTableSource interface for some TableSource 
> implementation that support nesting projection push-down.
> The interface could look as follows
> {code}
> def trait NestedFieldsProjectableTableSource {
>   def projectNestedFields(fields: Array[String]): 
> NestedFieldsProjectableTableSource[T]
> }
> {code}
> This interface works together with ProjectableTableSource 



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