entity Query drupal 8

entity Query

$query = \Drupal::entityQuery('attendance')
    ->condition('type', 'student_attendance_tracking', '=')
    // entity refernce field
    ->condition('field_course',  433, '>=');
    $courseRatings = $query->execute();
    return $courseRatings;

 // get all Course Ratings.
  function getCourseRatings($groupId) {
    $query = \Drupal::entityQuery('attendance')
    ->condition('type', 'student_attendance_tracking', '=')
    ->condition('field_course', $groupId, '=')
    ->condition('field_rfs', "" , '!=');
    $courseRatings = $query->execute();
    return $courseRatings;
  }

  // Sum of votes.  
  function getSumOfVotes($groupId) {
  // Aggregate query SUM,COUNT
    $query = \Drupal::entityQueryAggregate('attendance')
      ->condition('type', 'student_attendance_tracking', '=')
      ->condition('field_course',  $groupId, '=');
    $query->condition('field_rfs', '', '!=');
    $query->aggregate('field_rfs', 'sum');
    $sumOfVotes = $query->execute();
    if (isset($sumOfVotes['0']['field_rfs_sum'])) {
      return $sumOfVotes['0']['field_rfs_sum'];
    }
    return "";
  }


// group by query
  function getCourseRatingsStatistics($groupId) {
    $query = \Drupal::entityQueryAggregate('attendance')
      ->condition('type', 'student_attendance_tracking', '=');
    $query->condition('field_course', $groupId, '=');
    $query->groupBy('field_rfs');
    $query->condition('field_rfs', '', '!=');
    $query ->aggregate('field_rfs', 'count');
    $result = $query->execute();
    return $result;
  }