tp---查询连贯操作

                $car = M("Car");

        var_dump($car->select()); //返回所有数据的二维数组
        $attr = $car->where("brand=‘b002‘")->select();//where方法可以添加查询条件
        $attr = $car->table("Nation")->select();//table方法可以切换操作表
        $attr = $car->field("Code,Name")->select();//可以指定查询的字段
        $attr = $car->order("Oil desc")->select();//排序

        $attr = $car->limit(2,2)->select(); //分页查询，如果一个参数n的话就是取前n个

        $attr = $car->page(3,2)->select();//扩展，取第n页的几条数据

        $attr = $car->field("Brand,count(*)")->group("Brand")->select();//分组查询

        $attr = $car->join("Brand on Car.Brand = Brand.Brand_Code")->select();//连接查询

        $attr = $car->distinct(true)->field("Brand")->select();//去重

        $attr = $car->find();//根据主键取一条数据,不写主键值默认返回第一条
        $attr = $car->select("c001,c002"); //根据主键值查询，返回二维数组

        $attr = $car->where("Name like ‘%奥迪%‘")->order("Powers desc")->select();