MySQL的问题与工会/结合

表作者：

ID (INTEGER), 
author_name (VARCHAR), 
first_name (VARCHAR), 
last_name (VARCHAR), 
preferred_name (VARCHAR)

表合着：

ID (INTEGER) 
author1ID (INTEGER), 
author2ID (INTEGER), 
paper_ID (INTEGER) // (ID of the co-authored paper referenced by this link)

正如你可以看到，这两个表有一个'ID'列，但它们不相关。

然而，当我使用这个查询：

select author_name, count(*) as NumPapers from 
(select * from Author as a join CoAuthored as c on a.ID = c.author1ID 
union distinct 
select * from Author as b join CoAuthored as d on b.ID = d.author2ID) as t1 
group by author_name 
order by NumPapers;

MySQL的gves我一个错误说：ERROR 1060 (42S21): Duplicate column name 'ID'

为什么会出现这种情况，如何避免呢？

来源

2010-10-24 Michael L

而不是select * ...在正在联合的两个子查询中使用select author_name ...。该问题源于具有ID列的Author和CoAuthored。 SELECT *带来了这两个列，MySQL不喜欢这些联合使用这些产生具有两个相同名称列的结果集的想法。

来源

2010-10-24 22:09:28

试试这个：

select author_name, count(*) as NumPapers from 
(
    select a.id, a.author_name from Author as a 
    join CoAuthored as c on a.ID = c.author1ID 
    union distinct 
    select b.id, b.author_name from Author as b 
    join CoAuthored as d on b.ID = d.author2ID 
) as t1 
group by author_name 
order by NumPapers;

因为你不需要从合着的ID列，你可以只是没有在内部查询选择它。这应该删除重复的列错误，因为它只选择ID列中的一列。

来源

2010-10-24 22:10:07

这摆脱了这个问题，但现在NumPapers始终返回1.这是为什么？我使用了Will A的解决方案，并且保留了我的工会，而且它似乎工作正常。 – 2010-10-24 23:05:56

怎么样：

SELECT author_name, COUNT(*) AS NumPapers 
    FROM Author AS a 
    JOIN CoAuthored AS c ON a.ID = c.author1ID OR a.ID = c.author2ID 
GROUP BY author_name 
ORDER BY NumPapers;

来源

2010-10-24 22:13:39

MySQL的问题与工会/结合

回答

相关问题