插入带有计算列的语句

Question

I have created the following simple DataModel :

I used the following insert statements to insert values:

1) Table Products :

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

2) Table Orders :

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

All this works fine so far.

---

Now, in the table Products_per_Order I want to calculate the last column OrderValue by multiplying the Price with the Quantity . Therefore, I tried to go with the following two options referring to the answers here but could not make them work yet:

Note: The column Price is getting the prices based on the idProduct from the table Products .
This functionality already works. Only the multiplication with the quantity does not work.

Option 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));

Option 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;

Do you have any idea how to solve this issue?

Answer 1

You wrote that OrderValue is a calculated column, why not let the database calculate it for you?

Use alter table to change the OrderValue column to a generated column like this:

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

This way, you don't need to insert it at all - and your insert becomes like this:

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;

Answer 2

With reference to the comments below the question the issue is that the prices in the table Products need to be stored using . as the decimal separator instead of ,

If you modify the INSERT STATEMENT of the table Products to:

INSERT INTO test.products
(ProductName, Price)
VALUES 
("Product A","99.99"),
("Product B","49.95"), 
("Product C","5.95");

and then run the code in Option 2 everything works.

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;