作者相关书籍计数错误为什么以及如何解决？

Question

我在 SQL Server 2012 上工作，遇到一个问题：与作者相关的书籍计数错误。为什么与作者相关的书籍计数对于作者 Ahmed 是错误的？

当计算 author ahmed 时，我得到了一个不正确的结果，虽然它在书中有相关记录 table 作为 3 和 bookupdate 3 然后所有将是 6.

请问如何解决？

create table #books  
(  
    BookId int,  
    BookName nvarchar(200),  
    AuthorId  int  
)  

create table #booksUpdate  
(  
    BookId int,  
    BookName nvarchar(200),  
    AuthorId  int  
)  

insert into #booksUpdate  
values (119, 'matlab', 1), (120, '3dmax', 1), (121, 'c', 1)  

create table #Authors  
(  
    AuthorId int,  
    AuthorName nvarchar(200)  
)  

insert into #Authors  
values  (1, 'Ahmed'), (2, 'Mohamed'), (3, 'Eslam')  

insert into #books  
values (122, 'c#', 1), (233, 'Java', 1), 
       (555, 'c++', 1), (666, 'photoshop', 2),  
       (777, 'asp.net', 2), (888, 'python', 2)  
  
select 
    a.authorName, 
    count(b.BookName) as countBooks, 
    count(bu.BookName) as countBooksUpdate,
    (count(bu.BookName) + count(b.BookName)) as Total 
from 
    #Authors a   
left join 
    #books b on a.AuthorId = b.AuthorId  
left join 
    #booksUpdate bu on a.AuthorId = bu.AuthorId  
group by 
    a.authorName

输出：

authorName  countBooks  countBooksUpdate    Total  
--------------------------------------------------
Ahmed            9              9             18  
Eslam            0              0              0  
Mohamed          3              0              3

作者 Ahmed 的结果错误。

应该是

authorName  countBooks  countBooksUpdate    Total 
-------------------------------------------------
Ahmed            3                 3          6

如何将查询修正为 return 正确的结果？

预期结果是

authorName  countBooks  countBooksUpdate    Total  
-------------------------------------------------
Ahmed           3             3                6  
Eslam           0             0                0  
Mohamed         3             0                3

Answer 1

这行得通。它缺少 #books 和 #booksUpdate

之间 BookId 的连接

select a.authorName,count(b.BookName) as countBooks,
                    count(bu.BookName) as countBooksUpdate,
                   (count(bu.BookName) + count(b.BookName)) as Total
from #Authors a   
     left join #books b on a.AuthorId=b.AuthorId  
     left join #booksUpdate bu on a.AuthorId=bu.AuthorId  
                                  and b.BookId=bu.BookId
group by a.authorName;

结果

authorName  countBooks  countBooksUpdate    Total
Ahmed       3           0                   3
Eslam       0           0                   0 
Mohamed     3           0                   3

#booksUpdate table 中的 BookId 与#books table 中的任何一个都不匹配。没有 BookId 上的连接，查询正在执行交叉连接。

假设将#booksUpdate 中的 3 行更改为匹配 Ahmed 的 3 行。我在这里更改问题中发布的数据。

drop table if exists #booksUpdate;
go
create table #booksUpdate  
(  
BookId int,  
BookName nvarchar(200),  
AuthorId  int  
)  
insert into #booksUpdate  
values  
(122,'matlab',1),  
(233,'3dmax',1),  
(555,'c',1)

那么结果如下：

authorName  countBooks  countBooksUpdate    Total
Ahmed       3           3                   6
Eslam       0           0                   0
Mohamed     3           0                   3

作者相关书籍计数错误为什么以及如何解决？

count is wrong for author related book why and how to solve?

sql

tsql

stored-procedures

function

sql-server-2012