mysql - 插入带有计算列的语句

Question

我创建了以下简单的 DataModel :

我使用了以下insert statements插入值:

1) 表产品:

INSERT INTO test.products
(ProductName, Price)
VALUES 
("Product A","99,99"),
("Product B","49,95"), 
("Product C","5,95");

2) 表订单:

INSERT INTO test.orders
(Customer)
VALUES 
("Customer A"),
("Customer B"), 
("Customer B");

到目前为止，所有这些都运行良好。

<小时/>

现在，在表 Products_per_Order 中我想计算最后一列OrderValue乘以Price与 Quantity 。因此，我尝试使用以下两个选项来引用答案 here但还不能让它们工作:

注意:列 Price正在根据 idProduct 获取价格从表中Products 。
该功能已经可以使用了。仅与数量相乘不起作用。

选项 1:

INSERT INTO test.products_per_order
(Orders_idOrders, Products_idProducts, Price, Quantity, OrderValue)
VALUES
("1","1",(Select Price from test.products where test.products.idProducts = "1"),"5",(Price * Quantity)),
("1","2",(Select Price from test.products where test.products.idProducts = "2"),"4",(Price * Quantity)),
("2","1",(Select Price from test.products where test.products.idProducts = "1"),"10",(Price * Quantity)),
("3","2",(Select Price from test.products where test.products.idProducts = "2"),"3",(Price * Quantity)),
("3","3",(Select Price from test.products where test.products.idProducts = "3"),"9",(Price * Quantity));

选项 2:

INSERT INTO test.products_per_order 
(Orders_idOrders, Products_idProducts, Price, Quantity, OrderValue)
    SELECT m.idOrder, m.idProduct, p.price, m.qty, p.price * m.qty
    FROM (SELECT 1 as idOrder, 1 as idProduct, 5 as qty UNION ALL
          SELECT 1 as idOrder, 2 as idProduct, 4 as qty UNION ALL
          SELECT 2 as idOrder, 1 as idProduct, 10 as qty UNION ALL
          SELECT 3 as idOrder, 2 as idProduct, 3 as qty UNION ALL
          SELECT 3 as idOrder, 3 as idProduct, 9 as qty
         ) m
    LEFT JOIN test.products p on p.idProducts = m.idProduct;

您知道如何解决这个问题吗？

Answer 1

您写道 OrderValue 是一个计算列，为什么不让数据库为您计算它？

使用alter table将 OrderValue 列更改为生成的列，如下所示:

alter table test.products_per_order 
modify column OrderValue int generated always as (Price * Quantity) stored;

这样，您根本不需要插入它 - 并且您的插入内容将变成这样:

INSERT INTO test.products_per_order 
(Orders_idOrders, Products_idProducts, Price, Quantity)
    SELECT m.idOrder, m.idProduct, p.price, m.qty
    FROM (SELECT 1 as idOrder, 1 as idProduct, 5 as qty UNION ALL
          SELECT 1 as idOrder, 2 as idProduct, 4 as qty UNION ALL
          SELECT 2 as idOrder, 1 as idProduct, 10 as qty UNION ALL
          SELECT 3 as idOrder, 2 as idProduct, 3 as qty UNION ALL
          SELECT 3 as idOrder, 3 as idProduct, 9 as qty
         ) m
    LEFT JOIN test.products p on p.idProducts = m.idProduct;