如何选择1条记录和相关记录？

Question

我使用发布数据库，并保存书籍记录。书籍可以有多位作者。我们维护着一张表，其中记录了书籍的作者身份。我需要一个SQL查询来选择一个作者，然后选择在他们的每本书上使用它们的其他作者。

Authorship表格如下所示：

+---------+--------+
| Author  | BookID |
+---------+--------+
|    1    |    1   |
|    2    |    1   |
|    1    |    2   |
|    2    |    2   |
|    3    |    2   |
|    4    |    2   |
|    5    |    3   |
|    5    |    4   |
+---------+--------+

因此，如果我选择作者1，我希望看到他们合作的作者。结果将使我回复作者2,3和4。

这里的想法是，我可以为作者生成一份报告，说明他们在出版事业中与谁合作。

Answer 1

select a1.Author
from Authorship a
join Authorship a1 on a.BookID=a1.BookID
where a.Author=1

If you want to exclude the current author:

select a1.Author
from Authorship a
join Authorship a1 on a.BookID=a1.BookID
where a.Author=1 and a1.Author!=1

Answer 2

试试这个：

SELECT author
FROM AuthorsBooks 
WHERE bookid IN(SELECT bookid
                FROM AuthorsBooks
                WHERE author = 1);

SQL Fiddle Demo

这会给你：

| AUTHOR |
----------
|      1 |
|      2 |
|      3 |
|      4 |

或：使用JOIN：

SELECT DISTINCT b1.author
FROM AuthorsBooks AS b1
INNER JOIN AuthorsBooks AS b2  ON b1.bookid = b2.bookid
WHERE b2.author = 1;

SQL Fiddle Demo

Answer 3

  

这是你能做的。

SELECT DISTINCT Author  
FROM Authorship 
WHERE BookID IN(  
            SELECT BookID   
            FROM Authorship  
            WHERE Author = 1  
           ) 
AND Author <> 1

  

SQL FIDDLE DEMO