寫Mysql左連接不行？

Question

我有這個表

文章

articles_id

ARTICLE_NAME
article_qty
article_price
article_amount

訂單

orders_id
的article_id
INVOICE_ID
CUSTOMER_ID

客戶

customers_id
CUSTOMER_NAME
customer_position
customer_office

customer_invoice

當我做這樣的事情

$sql="SELECT customer_name, article_name FROM orders LEFT JOIN articles ON article_id = articles_id LEFT JOIN customers on customer_id = customers_id"; 

它doees沒有得到任何結果，什麼是留在一個查詢加入這個兩個表的正確方法？

我用CI 喜歡這個

$this->db->query($sql); 

什麼，我得到了我這個

object(CI_DB_mysql_result)#28 (8) { ["conn_id"]=> resource(31) of type (mysql link persistent) ["result_id"]=> resource(52) of type (mysql result) ["result_array"]=> array(0) { } ["result_object"]=> array(0) { } ["custom_result_object"]=> array(0) { } ["current_row"]=> int(0) ["num_rows"]=> int(2) ["row_data"]=> NULL } 

Answer 1

你需要指定任何表的別名加入你使用這樣的：

$sql="SELECT c.customer_name, a.article_name FROM orders o 
LEFT JOIN articles a ON o.article_id = a.articles_id 
LEFT JOIN customers c on o.customer_id = c.customers_id"; 

或者您可以使用USING語法：

$sql="SELECT c.customer_name, a.article_name FROM orders o 
LEFT JOIN articles a ON USING(articles_id) 
LEFT JOIN customers c on USING(customer_id);