Codeigniter加入表？

Question

我有表的這種結構：

Table Name: collisions 
Fields: id, creator1, creator2 
(1, 1, 2) - simple data in my sql table 

Table Name: creators 
Fields: id, artistname 
(1, john smith)- simple data in my sql table 
(2, steven michael)- simple data in my sql table 

我需要的是加入這些表，所以我可以得到藝術家的名字，而不是creator1 ID和創建者2的ID。

這是我迄今所做的：

$this->db->select('collisions.*, creators.artist_name AS cr1, creators.artist_name as cr2'); 
$this->db->join('creators', 'collisions.creator1 = cr1.id AND collisions.creator2 = cr2.id', 'left'); 
$data = $this->db->get('collisions')->result(); 

，但我收到此錯誤：

Unknown column 'cr1.id' in 'on clause' 

SELECT `collisions`.*, `creators`.`artist_name` AS cr1, `creators`.`artist_name` as cr2 FROM (`collisions`) LEFT JOIN `creators` ON `collisions`.`creator1` = `cr1`.`id` AND collisions.creator2 = cr2.id 

誰能告訴我什麼，我做錯了什麼？

Answer 1

該做的工作使用他們正在創造的問題alises

$this->db->select('collisions.*, cr1.artist_name as cr1, cr2.artist_name as cr2'); 
    $this->db->join('creators AS cr1', 'collisions.creator1 = cr1.id', 'left'); 
    $this->db->join('creators AS cr2', 'collisions.creator2 = cr2.id', 'left'); 
    $data = $this->db->get('collisions')->result(); 

Answer 2

請使用，而不是別名實際的表名：

$this->db->select('collisions.*, creators.artist_name AS cr1, creators.artist_name as cr2'); 
$this->db->join('creators', 'collisions.creator1 = creators.id AND collisions.creator2 = creators.id', 'left'); 
$data = $this->db->get('collisions')->result(); 

的原因，你不能使用別名是SQL的執行是按以下順序：

1)FROM clause 
2)WHERE clause 
3)GROUP BY clause 
4)HAVING clause 
5)SELECT clause 
6)ORDER BY clause 

，因爲你正在使用在中創建的別名選擇子句，在之後執行，其中子句。

這就是爲什麼你不能使用不存在的別名。