case class Student(name: String, age: Int,teacher:Teacher)
  case class Teacher(name:String,room:(Int,Int,Int),salary:Int)

  def main(args: Array[String]): Unit = {
    val teacher = Teacher("teacher-w",(1,2,3),99)
    val students = List(Student("a",11,teacher),Student("b",22,teacher))
    val benv = ExecutionEnvironment.getExecutionEnvironment
    benv.fromElements(students:_*).groupBy("name").sum("teacher.salary").print()
  }

以上这段代码会报错:

Fields 'teacher.salary' are not valid for 'com.lx.list.List1$Student(name: String, age: Integer, teacher: com.lx.list.List1$Teacher(name: String, room: scala.Tuple3(_1: Integer, _2: Integer, _3: Integer), salary: Integer))'.

但是如果把groupBy换成keyBy就可以执行了。请问这是什么原因？