.env文件中默认有两个DB_HOST，其中一个被注释掉了，则两个有啥区别？

.env文件下：

将127.0.0.1的注释掉，保留mysql的，可以连接上数据库，也可以对数据库进行 CURD，但是php artisan migrate会报错：

vagrant@homestead:~/projects/demo$ php artisan migrate

   Illuminate\Database\QueryException 

  SQLSTATE[HY000] [2002] php_network_getaddresses: getaddrinfo failed: Temporary failure in name resolution (SQL: select * from information_schema.tables where table_schema = demo and table_name 
= migrations and table_type = 'BASE TABLE')

  at vendor/laravel/framework/src/Illuminate/Database/Connection.php:678
    674▕         // If an exception occurs when attempting to run a query, we'll format the error
    675▕         // message to include the bindings with SQL, which will make this exception a
    676▕         // lot more helpful to the developer instead of just the database's errors.
    677▕         catch (Exception $e) {
  ➜ 678▕             throw new QueryException(
    679▕                 $query, $this->prepareBindings($bindings), $e
    680▕             );
    681▕         }
    682▕ 

      +33 vendor frames 
  34  artisan:37
      Illuminate\Foundation\Console\Kernel::handle()

而把mysql的注释掉，保留127.0.0.1的，就不会出现问题。
这两者有啥区别吗？为什么会出现这种情况？