Codeigniter：ORDER BY CASE 查询出错

这是我的查询代码点火器

$this->db->select('p.*,u.firstname, u.lastname,s.title AS industry, pt.type_name , al.length_value',FALSE);
$this->db->from($this->_tbl_projects . ' as p');
$this->db->join($this->_tbl_client_details . ' as c', 'c.id = p.client_id', 'left');
$this->db->join($this->_tbl_users . ' as u', 'u.id = c.user_id', 'left');
$this->db->join($this->_tbl_project_types . ' as pt', 'pt.project_type_id = p.project_type_id', 'left');
$this->db->join($this->_tbl_specializations . ' as s', 's.specialization_id = p.specialization_id', 'left');
$this->db->join($this->_tbl_article_length . ' as al', 'al.article_length_id = p.article_length_id', 'left');
$this->db->order_by("CASE p.submit_to
                                    WHEN '' THEN 0
                                    WHEN 'writer' THEN 1
                                    ELSE 2
                                END, p.request_end_date asc",FALSE);

打印出来

SELECT p.*, u.firstname, u.lastname, s.title AS industry, pt.type_name, al.length_value 
FROM (`projects` as p) 
LEFT JOIN `client_details` as c ON `c`.`id` = `p`.`client_id` 
LEFT JOIN `users` as u ON `u`.`id` = `c`.`user_id` 
LEFT JOIN `project_types` as pt ON `pt`.`project_type_id` = `p`.`project_type_id` 
LEFT JOIN `specializations` as s ON `s`.`specialization_id` = `p`.`specialization_id` 
LEFT JOIN `article_length` as al ON `al`.`article_length_id` = `p`.`article_length_id` WHERE `p`.`client_id` = '26' AND `p`.`status` IN (2, 3) 
ORDER BY 
        `CASE` p.submit_to 
            WHEN '' THEN 0 
            WHEN 'writer' THEN 1 
            ELSE 2 
         END, `p`.`request_end_date` asc

在打印的查询中，CASE打印者`CASE`，所以sql会抛出错误。

我该如何解决？

Submit_to字段的结构是

  submit_to enum('','writer','students') NOT NULL

CodeIgniter 文档指出 Active Record 类不支持 order by 子句中的 case 语句。我建议重构 SQL 调用，以便 case 语句成为 select 子句的一部分。像下面这样的东西应该可以解决问题。

$this->db->select("p.*,u.firstname, u.lastname,s.title AS industry, pt.type_name, al.length_value, CASE p.submit_to WHEN 'writer' THEN 2 WHEN 'students' THEN 1 ELSE 0 END AS ordered_submit_to",FALSE);
$this->db->from($this->_tbl_projects . ' as p');
$this->db->join($this->_tbl_client_details . ' as c', 'c.id = p.client_id', 'left');
$this->db->join($this->_tbl_users . ' as u', 'u.id = c.user_id', 'left');
$this->db->join($this->_tbl_project_types . ' as pt', 'pt.project_type_id = p.project_type_id', 'left');
$this->db->join($this->_tbl_specializations . ' as s', 's.specialization_id = p.specialization_id', 'left');
$this->db->join($this->_tbl_article_length . ' as al', 'al.article_length_id = p.article_length_id', 'left');
$this->db->order_by('ordered_submit_to', 'ASC');
$this->db->order_by('p.request_end_date', 'ASC');