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

    https://github.com/apache/flink/pull/3063#discussion_r95308316
  
    --- Diff: 
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/plan/logical/operators.scala
 ---
    @@ -92,20 +92,19 @@ case class Project(projectList: Seq[NamedExpression], 
child: LogicalNode) extend
       }
     
       override protected[logical] def construct(relBuilder: RelBuilder): 
RelBuilder = {
    -    val allAlias = projectList.forall(_.isInstanceOf[Alias])
         child.construct(relBuilder)
    -    if (allAlias) {
    -      // Calcite's RelBuilder does not translate identity projects even if 
they rename fields.
    -      //   Add a projection ourselves (will be automatically removed by 
translation rules).
    -      val project = LogicalProject.create(relBuilder.peek(),
    +    // Calcite's RelBuilder does not translate identity projects even if 
they rename fields.
    +    // We add a projection ourselves (will be automatically removed by 
translation rules).
    +    val project = LogicalProject.create(
    --- End diff --
    
    Good point !  The hack code existed because of Calcite's RelBuilder does 
not create  project when only rename fields.  The `project( Iterable<? extends 
RexNode> nodes, Iterable<String> fieldNames, boolean force)` was introduced and 
fixed this issue by Calcite-1342. 
    
    I have tried to replace the hack code by the following code, and all tests 
passed !
    
    ```scala
    override protected[logical] def construct(relBuilder: RelBuilder): 
RelBuilder = {
        child.construct(relBuilder)
        relBuilder.project(
          projectList.map {
            case Alias(c, _, _) => c.toRexNode(relBuilder)
            case n@_ => n.toRexNode(relBuilder)
          }.asJava,
          projectList.map(_.name).asJava,
          true)
    }
    ```
    
     


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