左联子表：

LEFT JOIN ( SELECT * FROM 'order_efali` ORDER BY `id` DESC ) AS ohe ON `ohe`.`number` = `o`.`number` 

TP写法：

 
            $rrc= Db::name('order_history')
            ->order('id desc')
            ->buildSql();
 
            $rsu = Db::name('order')
                ->alias('o')
                ->leftjoin('user u', 'u.id=o.user_id')
                ->leftjoin($rrc.' as ohe ', 'ohe.number=o.number')
                ->group('o.number') //去重
                ->limit($limit)
                ->page($params['page'])
                ->field('o.*,u.nickname')
                ->select();