sql-server - 如何创建一个计算列来引用另一个表中的另一列？

Question

我正在使用 Microsoft SQL Server，而且我还在学习。我有两个表，一个产品表和一个订单明细表。产品表包含价格，然后订单明细表包含对产品、产品数量和总价的引用。这是两个表:

--Create Product Table
CREATE TABLE Products.Product  
(
    product_id          INT             NOT NULL    PRIMARY KEY IDENTITY,
    product_name        VARCHAR(40)     NOT NULL,
    product_desc        VARCHAR(5000),
    product_price       SMALLMONEY      NOT NULL    CHECK (product_price >= 0)
);

--Create Order Details Table
CREATE TABLE Orders.Order_detail 
(
    order_detail_id     INT             NOT NULL    PRIMARY KEY IDENTITY,
    product_id          INT             NOT NULL,
    product_quantity    INT             NOT NULL    CHECK (product_quantity >= 0),
    order_detail_total  MONEY           NOT NULL,

    FOREIGN KEY (product_id)        REFERENCES Products.Product
);

我怎样才能使 order_detail_total 成为一个计算列，即 product_price * product_quantity？

Answer 1

感谢@Andy K，我想出了这个解决方案:

--Create Product Table
CREATE TABLE Products.Product  
(
    product_id          INT             NOT NULL    PRIMARY KEY IDENTITY,
    product_name        VARCHAR(40)     NOT NULL,
    product_desc        VARCHAR(5000),
    product_price       SMALLMONEY      NOT NULL    CHECK (product_price >= 0)
);
GO

--Create a function to calculate the order details total
CREATE FUNCTION Orders.calcOrderDetailTotal(@quantity INT, @productId INT)
RETURNS MONEY
AS
BEGIN
    DECLARE @price SMALLMONEY
    SELECT @price = product_price FROM Products.Product AS TP 
           WHERE TP.product_id = @productId
    RETURN @quantity * @price
END
GO

--Create Order Details Table
CREATE TABLE Orders.Order_detail 
(
    order_detail_id     INT             NOT NULL    PRIMARY KEY IDENTITY,
    product_id          INT             NOT NULL,
    product_quantity    INT             NOT NULL    CHECK (product_quantity >= 0),
    order_detail_total  MONEY           NOT NULL,

    FOREIGN KEY (product_id)        REFERENCES Products.Product
);

这在我创建的测试数据库上对我有用。