建議創建做多表的聯合時，一個唯一的ID

Question

我有這樣

CREATE VIEW PEOPLE 

AS 

SELECT CustomerId, CustomerName FROM Customers 
UNION ALL 
SELECT EmployeeId, EmployeeName FROM Employees 
UNION ALL 
SELECT FriendId, FriendName From Friends 

現在我需要添加唯一ID的觀點，自然是因爲我可以有一個CustomerId = 15，並提出了看法一個EmployeeID = 15

所以我做的訣竅是以下

SELECT 
    CAST('1' + CAST(CustomerId AS VARCHAR(30)) AS INT) as UniqueCustomerId, 
CustomerId, CustomerName FROM Customers 
UNION ALL 
SELECT 
    CAST('2' + CAST(EmployeeId AS VARCHAR(30)) AS INT) as UniqueEmployeeId, 
EmployeeId, EmployeeName FROM Employees 
UNION ALL 
SELECT 
    CAST('3' + CAST(FriendId AS VARCHAR(30)) AS INT) as UniqueFriendId, 
FriendId, FriendName From Friends 

反正這個鑄件varchar(30)和回int是一個開銷，因爲我有很多記錄。

你能提出一個更好的方法嗎？

Answer 1

如果你得有一個ID，只是做數學：

SELECT 1000000 + CustomerID AS UniqueCustomerId 
     , CustomerId 
     , CustomerName 
FROM Customers 
UNION ALL 
SELECT 2000000 + EmployeeId AS UniqueEmployeeId 
     , EmployeeId 
     , EmployeeName 
FROM Employees 
UNION ALL 
SELECT 3000000 + FriendId AS UniqueFriendId 
     , FriendId 
     , FriendName 
FROM Friends 

Answer 2

這應該很好地工作：

CREATE VIEW PEOPLE AS 
SELECT CustomerId, null as EmployeeId, null as FriendId, CustomerName FROM Customers 
UNION ALL 
SELECT null, EmployeeId, null, EmployeeName FROM Employees 
UNION ALL 
SELECT null, null, FriendId, FriendName From Friends 

Answer 3

我喜歡這種方法，因爲它仍然可以使用索引上在客戶，僱員和FriendID

SELECT 1 [PersonType],CustomerId [PersonId], CustomerName [PersonName] FROM Customers 
UNION ALL 
SELECT 2, EmployeeId, EmployeeName FROM Employees 
UNION ALL 
SELECT 3, FriendId, FriendName From Friends