Question

我在SQL Server中有一个表Authors，其中Author_ID为主键。

Authors表格结构

Author_ID | Author_Name  
----------------------------
677       | Nuno Vasconcelos
1359      | Peng Shi
6242      | Z. Q. Shi  
...       | ...  
...       | ...

我有另一个表CoAuthors，其中CoAuthor_ID为主键，Author_ID为外键。

CoAuthors表格结构

CoAuthor_ID | CoAuthor_Name | Author_ID  
---------------------------------------
47          | Jim Bezdek    | NULL
111         | Vishal Gupta  | NULL
318         | Muaz A. Niazi | NULL
...         | ...           | ...  
...         | ...           | ...

我有另一个Author-CoAuthor映射表Yearly_Author_CoAuthors：

Author_ID | CoAuthor_ID | Year
------------------------------
677       | 901706      | 2005
677       | 838459      | 2007
677       | 901706      | 2007  
...       | ...         | ...  
...       | ...         | ...

现在我必须在来自CoAuthors表的Authors表中插入外键。问题是，对于Author_ID，我可能有CoAuthor_ID的多个值，例如执行此查询：

SELECT   
    Author_ID, CoAuthor_ID, Year  
FROM     
    Yearly_Author_CoAuthors  
WHERE
    CoAuthor = 901706  
ORDER BY 
    Author_ID, Year, CoAuthor_ID

我得到了这个输出：

Author_ID | CoAuthor_ID | Year  
------------------------------
677       | 901706      | 2005
677       | 901706      | 2007
677       | 901706      | 2009
1683703   | 901706      | 2012

显示CoAuthor_ID = 901706有两个DISTINCT Author_ID，所以这里：

如何在Author_ID表中插入CoAuthors作为外键约束？

Answer 1

只要Author_ID在authors表中是唯一的，作者和共同作者之间潜在的多对多关系就不会阻止外键约束。只需这样做：

ALTER TABLE CoAuthors
ADD CONSTRAINT FK_Authors_Author_ID FOREIGN KEY (CoAuthor_ID) 
    REFERENCES Authors (Author_ID)

Answer 2

查看示例Yearly_Author_CoAuthors选择查询，您必须输入重复值才能返回它们。

制作Author_ID＆amp; CoAuthor_ID复合主键（不含年份）或在这两列中添加唯一索引。

编辑：如果你在Yearly_Author_CoAuthors.Author_ID和Yearly_Author_CoAuthors.CoAuthor_ID上没有外键，那么我首先建议你在user3481891的答案中调整脚本，将它们添加到该表中。然后，我不明白为什么你不能查询你已有的东西。以下是一些例子（未经测试的我害怕，如果他们不工作，请告诉我）：

-- to get list of who a CoAuthor has worked with and when
select  a.Author_Name,
        ca.CoAuthor_Name,
        [Year]
from    Authors a inner join 
        Yearly_Author_CoAuthors yac on a.Author_ID = yac.Author_ID inner join 
        CoAuthors ca on yac.CoAuthor_ID = ca.CoAuthor_ID
where   yac.CoAuthor = 901706

-- to get a list of first occasions when a CoAuthor has worked with each Author
select  a.Author_Name,
        ca.CoAuthor_Name,
        min([Year]) as FirstCollaborationDate
from    Authors a inner join 
        Yearly_Author_CoAuthors yac on a.Author_ID = yac.Author_ID inner join 
        CoAuthors ca on yac.CoAuthor_ID = ca.CoAuthor_ID
where   yac.CoAuthor = 901706
group by a.Author_Name,
        ca.CoAuthor_Name
order by min([Year])

如何在SQL Server

2 个答案: