选择记录顺序为另一个表的计数，而不是在Mysql中检索正确的计数

Question

在mysql db中，我有两个表book和ratingtable。

书籍表有三个字段ID,uniqueid,Title

评级表有三个字段Book_ID,userid,rating

我需要一个检索记录group by id（书表）和order by count(rating)（评级表）的查询。

我尝试了这样的查询：

SELECT book.ID,book.Title,COUNT(ratingtable.rating) AS views
FROM book LEFT JOIN ratingtable ON book.ID = ratingtable.book_ID
GROUP BY book.ID
ORDER BY views DESC

但是对于三个值，它显示错误的计数值。我不知道会发生什么。

修改 ratingtable：

书：

这里答案[count（rating）]应为1。但它显示

帮我解决这个问题。

Answer 1

您获得的结果实际上非常正确，因为您的图书ID不是唯一的。但是，要获得您想要的计数，您可以使用子查询首先对书籍进行分组，然后进行计数：

SELECT b2.ID, b2.Title,COUNT(ratingtable.rating) AS views
FROM 
    (SELECT b1.id, b1.title FROM Book b1 Group by b1.id, b1.title) b2 
LEFT JOIN ratingtable ON b2.ID = ratingtable.book_ID
GROUP BY b2.ID, b2.Title
ORDER BY views DESC

Answer 2

您需要按书名和标题进行分组。

SELECT book.ID, book.Title, COUNT(ratingtable.rating) AS views
FROM book LEFT JOIN ratingtable ON book.ID = ratingtable.book_ID
GROUP BY book.ID, book.Title
ORDER BY views DESC

或使用相关的子查询来计算：

select distinct book.ID,
                book.Title,
                (select count(*) from ratingtable
                 where book.ID = ratingtable.book_ID) as views
from book
ORDER BY views DESC