Codeigniter:ORDER BY CASE查询出错

Question

这是我在Codeigniter中的查询

$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

在打印查询中,CASE由`CASE`打印,因此sql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

Answer 1

CodeIgniter文档表明Active Record类中不支持order by子句中的case语句.我建议重构SQL调用,以便case语句是select子句的一部分.像下面这样的东西应该做的伎俩.

$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');

Answer 2

我在 SO 上的另一个答案中找到了一个很好的解决方案，因此如果您已登陆此页面但未找到该页面，我将在此处重新发布。

如果将 case 语句括在括号中，则可以使用 case 语句。

$this->db->order_by("
    (CASE p.submit_to
        WHEN '' THEN 0
        WHEN 'writer' THEN 1
        ELSE 2
    END), 
    p.request_end_date asc"
);