在模型中也可以調用數據庫的聚合方法進行查詢，例如：

靜態調用：

User::count();
User::where('status','>',0)->count();
User::where('status',1)->avg('score');
User::max('score');

動態調用：

$user = new User;
$user->count();
$user->where('status','>',0)->count();
$user->where('status',1)->avg('score');
$user->max('score');