平均计算codeigniter查询

Question

我正在尝试查找平均速率，但低于 codeigniter 查询结果错误 "Unknown column 'prate' in 'field list'"

 $this->db->select('AVG(prate)as avgprate');
        $this->db->from('stock','(select sum((pdetails.quantity*pdetails.rate)/pdetails.quantity) AS prate FROM `stock` INNER JOIN `pdetails` ON `pdetails`.`stock_id` = `stock`.`stock_id`)');

        $result = $this->db->get();
        $res = $result->row();

我该如何解决这个问题

Answer 1

$this->db->select('AVG(t.prate)as avgprate');
        $this->db->from('stock ,(select sum((pdetails.quantity*pdetails.rate)/pdetails.quantity) AS prate FROM `stock` INNER JOIN `pdetails` ON `pdetails`.`stock_id` = `stock`.`stock_id`)t');

        $result = $this->db->get();
        $res = $result->row();