对于拥有两名作者的每本书，其精选书名，出版商名称，类型和作者名称均无结果

Question

我想获取有2位作者的书的详细信息，为此，我写了以下查询。

SELECT BOOK.Book_Title
     , PUBLISHER.Publisher_Name
     , BOOK.Book_Type 
     , AUTHOR.Author_Last
     , AUTHOR.Author_First 
  FROM AUTHOR
     , WROTE
     , BOOK
     , PUBLISHER 
 WHERE AUTHOR.Author_Num = WROTE.Author_Num 
   AND WROTE.Book_Code = BOOK.Book_Code 
   AND BOOK.Publisher_Code = PUBLISHER.Publisher_Code
HAVING COUNT(WROTE.Book_Code) = 2;

但是当我运行它时，我得到了0行返回。尽管表格中有可用的数据，但有几行，其中有2位作者反对一本书。

这是我要在其中应用查询的架构。

以下是WROTE表中可用的数据，它是BOOK和AUTHOR表的多对多关系。

请告诉我问题出在哪里？

Answer 1

您的查询不正确，因为在尝试应用假设具有某些分组字段的HAVING条件时，它没有GROUP BY部分。

我想使用以下查询（MS SQL）：

SELECT bk.Book_Title
     , pb.Publisher_Name
     , bk.Book_Type 
     , auth.Author_Last
     , auth.Author_First 
  FROM AUTHOR as auth
        join WROTE as wr on auth.Author_Num = wr.Author_Num
        join BOOK as bk on wr.Book_Code = bk.Book_Code
        join PUBLISHER as pb on bk.Publisher_Code = pb.Publisher_Code
where exists (SELECT 1 
                from  WROTE as wr_ex
                where wr_ex.Book_Code = wr.Book_Code
                group by wr_ex.Book_Code
                having count(1) = 2 )

可能有一个子查询的变体，该子查询在FROM部分中选择有2位作者的Book_codes，应该通过加入所有其他内容来关注