Sql 使用GROUP BY从多个表中选择

我对多任务查询有点小问题。（关系数据库管理系统：访问）

以下是数据库模式：（此查询中仅使用S_卡、书籍、作者、学生表） S_卡是学生图书订单（在图书馆）

查询： 选择学生中最受欢迎的作者以及该作者在图书馆订购的书籍数量

虽然我可以在一次查询中获得订单+作者列表，但如下所示：

SELECT 
    Students.FirstName & " " & Students.LastName AS [Student], 
    Books.Name AS [Book], Authors.FirstName & " " & Authors.LastName AS [Author]
FROM 
    Students, 
    Books, 
    S_Cards, 
    Authors
WHERE 
    S_Cards.ID_Student = Students.ID 
AND S_Cards.ID_Book = Books.ID 
AND Books.ID_Author = Authors.ID
ORDER BY Authors.LastName

结果（对不起，是俄语）：

我不明白，为什么我不能像这样计数和分组：

SELECT 
    Students.FirstName & " " & Students.LastName AS [Student], 
    Books.Name AS [Book], 
    COUNT(Authors.FirstName & " " & Authors.LastName) AS [Number of books]
FROM Students, Books, S_Cards, Authors
WHERE 
    S_Cards.ID_Student = Students.ID 
AND S_Cards.ID_Book = Books.ID 
AND Books.ID_Author = Authors.ID
GROUP BY 3

我得到一个错误，“Authors.FirstName&&&Authors.LastName”不是静态函数或组的一部分

问题:

有没有一种方法可以在不使用联接的情况下，仅通过GROUP by、SELECT、UNION和how进行查询

我的第二个问题是什么

SQL Server中的字符串是

+

而不是

&

。此外，还应按非聚合函数的对象进行分组

SELECT Students.FirstName + ' ' + Students.LastName AS [Student]
     , Books.Name AS [Book]
     , COUNT(Authors.FirstName + ' ' + Authors.LastName) AS [Number of books]
  FROM Students
  JOIN S_Cards
    ON S_Cards.ID_Student = Students.ID
  JOIN BOOKS
    ON S_Cards.ID_Book = Books.ID 
  JOIN Authors
    ON Books.ID_Author = Authors.ID
 GROUP BY Students.FirstName + ' ' + Students.LastName
        , Books.Name

请注意，我已将您的查询更改为标准ANSI join语法，这使得错误更难产生，也更易于阅读

---

想想看，你的计数似乎有点奇怪。图书的数量不是计数（books.ID）？

您必须根据不属于聚合函数的任何内容进行分组：

SELECT 
    Students.FirstName & " " & Students.LastName AS [Student], 
    Books.Name AS [Book], 
    COUNT(Authors.FirstName & " " & Authors.LastName) AS [Number of books]
FROM Students, Books, S_Cards, Authors
WHERE 
    S_Cards.ID_Student = Students.ID 
AND S_Cards.ID_Book = Books.ID 
AND Books.ID_Author = Authors.ID
GROUP BY Students.FirstName & " " & Students.LastName, 
    Books.Name AS [Book]

我建议您开始使用显式连接而不是隐式连接。在大多数情况下，MS Access有更好的选择

<...>
FROM Students
INNER JOIN S_Cards
ON Students.ID = S_Cards.ID_Student

来自学生
内部连接S_卡
关于Students.ID=S_卡。ID_学生

或

来自学生
左加入S_卡
关于Students.ID=S_卡。ID_学生

查询设计窗口将允许您使用正确的语法构建联接。只需将联接字段从一个表拖放到下一个表，然后选择所需的联接类型。

解决方案（从中提取）：

---

这假设您使用的是SQL Server（看起来是这样的）。请在将来总是用适当的RDBMS标记问题。谢谢回复。我认为COUNT（Books.ID）会计算某本书的订购次数。我需要数一数作者的书被订购了多少次，而不是某一本书。RDBMS是一种访问。

<...>
FROM Students
LEFT JOIN S_Cards
ON Students.ID = S_Cards.ID_Student

SELECT TOP 1 Author, COUNT(Book) AS [Number of books] FROM
(
    SELECT 
        Students.FirstName & " " & Students.LastName AS [Student], 
        Books.Name AS [Book], 
        Authors.FirstName & " " & Authors.LastName AS [Author]
    FROM 
        Students, 
        Books, 
        S_Cards, 
        Authors
    WHERE 
        S_Cards.ID_Student = Students.ID AND
        S_Cards.ID_Book = Books.ID AND
        Books.ID_Author = Authors.ID
    ORDER BY Authors.LastName
)
GROUP BY Author
ORDER BY 2 DESC