优化后台学生导出功能

@@ -252,9 +252,9 @@ class Study extends Backend
                     ->setCellValue('F1', '手环ID')
                     ->setCellValue('G1', '总积分');
                 if ($ids == 'all' || empty($ids)) {    //判断当前数据为全部或者选中的
-                    $list = $this->model->with('school,grade')->select();
+                    $list = $this->model->select();
                 } else {
-                    $list = $this->model->with('school,grade')->select($ids);
+                    $list = $this->model->select($ids);
                 }
 
                 foreach ($list as $k => $val) {