計算列（微軟的SQL Server 2014）

Question

書

| B_ID | Name | Unit_Price| 
|------+---------+-----------| 
| B01 | Math |  25 | 
| B02 | Science |  34 | 

訂購

| O_ID | B_ID | Quantity |Total_Price| 
|------+------+-----------+-----------| 
| O01 | B01 |  2  |  ?  | 
| O02 | B02 |  5  |  ?  | 

我怎樣才能乘以Order.Quantity和Book.Unit_Price其中Order.B_ID是一個FK得到TOTAL_PRICEBook.B_ID。謝謝！

Answer 1

您可以創建一個函數，其中計算列將使用該功能。

CREATE FUNCTION dbo.GetTotalPrice(INT @id) 
RETURNS DECIMAL(19,4) 
AS 
BEGIN 
    DECLARE @ret DECIMAL(19,4) 
    SELECT @ret = O.Quantity * B.Unit_Price 
       FROM Order O 
        INNER JOIN Book B 
        ON O.B_ID = B.B_ID 
        WHERE B.B_ID = @id 
      IF (@ret IS NULL) 
      SET @ret = 0 
      RETURN @ret 
END 

ALTER TABLE dbo.Order 
    ADD Total_Price AS dbo.GetTotalPrice(O_ID) 

Answer 2

像你需要創建更多的聲音一個VIEW：

CREATE VIEW dbo.OrderPrice 
AS 

SELECT O.O_ID, 
     O.B_ID, 
     O.Quantity, 
     O.Quantity * B.Unit_Price Total_Price 
FROM Order O 
INNER JOIN Book B 
    ON O.B_ID = B.B_ID;