寻找失踪的连接表的SQL Server记录

Question

比方说，我在SQL Server 2008中，Users，Site和UserSite 3个表：

+-------+ +-------+ +-------------+ 
| User | | Site | | User Site | 
+-------+ +-------+ +-------------+ 
| User1 | | Site1 | | User1 Site1 | 
| User2 | | Site2 | | User1 Site2 | 
| User3 | +-------+ | User1 Site3 | 
+-------+     | User2 Site1 | 
          | User2 Site3 | 
          | User3 Site1 | 
          +-------------+ 

期望的结果：对于每个User和Site组合必须有一个记录在UserSite这样的：

+-------------+ 
| User Site | 
+-------------+ 
| User1 Site1 | 
| User1 Site2 | 
| User1 Site3 | 
| User2 Site1 | 
|*User2 Site2*| Inserted 
| User2 Site3 | 
| User3 Site1 | 
|*User3 Site2*| Inserted 
|*User3 Site3*| Inserted 
+-------------+ 

我只能插入新记录，并且不能从头改写表。

有没有办法与SQL Server做到这一点？

Answer 1

我可能会提出一个强力方法。截断表，然后插入所有的值：

truncate table UserSite; 

insert into UserSite(User, Site) 
    select u.user, s.site 
    from users u cross join sites s; 

你可以只用一个稍微复杂的查询添加新的：

insert into UserSite(User, Site) 
    select u.user, s.site 
    from users u cross join 
     sites s 
    where not exists (select 1 
         from usersite us 
         where us.user = u.user and us.site = s.site 
        ); 

Answer 2

使用CROSS JOIN

SELECT 
* 
FROM Users 
CROSS JOIN Site 

Answer 3

如果你只想选择缺失的记录，试试这个：

SELECT * 
FROM Users 
CROSS JOIN Site 

EXCEPT 

SELECT * 
FROM UserSite