Question

所以我试图建立一个小型网上商店。我有2个表：cart_products和order_products。在这些表格中，有两种类型的商品可以添加到购物车中：promotion和products。这两种类型的项目存储在名为promotions和products的不同表中。

最初，所有产品/促销都会添加到cart表中，一旦用户签出，它们就会转移到orders表并从cart表中删除。

如果所选项目是产品，则promotion_id值默认设置为0。如果所选项目是促销，则反之亦然。这是我的基本结构：

cart_products

----------------------------------------------------------------------------------
| cart_products_id |    cart_id    |   product_id | promotion_id      | quantity |
----------------------------------------------------------------------------------
| 6                |       1       |   5          | 0                 | 2  
---------------------------------------------------------------------------------

order_products

----------------------------------------------------------------------------------
| order_id |   user_id    | product_id | promotion_id      | price    | quantity |
----------------------------------------------------------------------------------

我遇到的问题是尝试LEFT JOIN产品/促销活动以获取所选商品的price。这是我目前的询问。

INSERT INTO order_details (order_id, user_id, product_id, promotion_id, price, quantity)
VALUES(
  '6', 
  '7',
  (SELECT 
    cart_products.product_id, 
    cart_products.promotion_id,
    IF(cart_products.promotion_id = '0', products.price, promotions.price),
    cart_products.quantity

  FROM cart_products


  LEFT JOIN products
  ON cart_products.product_id = products.product_id

  LEFT JOIN promotions
  cart_products.promotion_id = promotions.promotion_id

  WHERE cart_products.cart_id = '6')
)

然而，这给了我一个错误Not unique table/alias。有谁知道我怎么能这样做？非常感谢任何帮助！

Answer 1

您可以简单地选择常量，以便您可以使用INSERT INTO SELECT语法，而不是像您一样定义值：

INSERT INTO order_details (order_id, user_id, product_id, promotion_id, price, quantity)
SELECT (
    '6', 
    '7',
    cart_products.product_id, 
    cart_products.promotion_id,
    IF(cart_products.promotion_id = '0', products.price, promotions.price),
    cart_products.quantity
  FROM cart_products
  LEFT JOIN products
    ON cart_products.product_id = products.product_id
  LEFT JOIN promotions
    ON cart_products.promotion_id = promotions.promotion_id
  WHERE cart_products.cart_id = '6'
)

另外，我相信你在第二次左连接中忘记了“ON”条款

将数据从一个表插入另一个表 - MySQL

1 个答案: