MySQL仅在[重复]时将表连接到另一个表

Question

我在这里有一个有点复杂的查询。我必须按名称选择列，而不仅仅是用户的订单。*。因为我有来自不同表的多个同名列。

我要做的是从订单、用户、payment_methods_translation 中选择特定字段并仅在 orders.payment_method_id = '3' 时加入 bank_accounts_translation

SELECT 
   orders.id as orderid,
   orders.final_total,
   orders.user_id,
   orders.auto_cancel,
   users.id as userid,
   users.first_name,
   payment_methods_translation.payment_method_id,
   payment_methods_translation.name 
FROM 
   orders,users, 
   payment_methods_translation
WHERE
   orders.id='$id' AND 
   orders.user_id = users.id AND
   orders.payment_method_id = payment_methods_translation.payment_method_id AND 
   orders.auto_cancel='1' 
JOIN 
   bank_accounts_translation ON (orders.payment_method_id='3' 
   AND orders.bank_id = bank_accounts_translation.bank_account_id)

但是我得到一个 mysql 错误。那么，只有当 orders.payment_method_id = '3' 和 orders.bank_id = bank_accounts_translation.bank_id 时，我才能从 bank_accounts_translation 中选择所有字段

Answer 1

左连接应该这样做......我

• 重构代码以使用当前的 ANSI 标准，您似乎在混合使用它们。
• 使用表别名来提高可读性。

LEFT JOIN 表示返回之前列出的表中的所有记录，并且只返回那些与要加入的表的 on 条件匹配的记录。

SELECT O.id as orderid
      ,O.final_total
      ,O.user_id
      ,O.auto_cancel
      ,u.id as userid
      ,u.first_name
      ,PMT.payment_method_id
      ,PMT.name 
FROM orders O
INNER JOIN users U
   ON O.user_id = U.id 
INNER JOIN payment_methods_translation  PMT
   ON O.payment_method_id = PMT.payment_method_id 
LEFT JOIN bank_accounts_translation  BAT
   ON O.payment_method_id='3' 
  and O.bank_id = BAT.bank_account_id
WHERE O.id='$id' 
  and O.auto_cancel='1'