MySQL PDO Query不显示过程输出变量

Question

我想在PDO设置中使用过程获取out变量。我得到一个空数组（）;

      $connection->query('
       drop procedure if exists relatives;
       create procedure relatives(in parent int(11),out counted int(11))
       begin
        set @counted=1;
       end;
      ');
      $fetch=$connection->query('call relatives(1,@counted); select @counted as c;')->fetchall();