17-2 異動資料表

1. 建立異動資料表用的migration

   php artisan make:migration add_tests_cols --table=tests

2.  編輯\專案\database\migrations\2018_08_10_001435_add_tests_cols.php：

   public function up()
   {
       Schema::table('tests', function (Blueprint $table) {
           $table->unsignedTinyInteger('grade');
           $table->unsignedTinyInteger('class');
           $table->unsignedTinyInteger('num');
       });
   }

   以及

   public function down()
   {
       Schema::table('tests', function (Blueprint $table) {
           $table->dropColumn(['grade', 'class', 'num']);
       });
   }