1

考虑 BOOKSTORE 数据库的以下数据库模式：

Books (bookid, title, author, year)
Customers (customerid, name, email)
Purchases (customerid, bookid, year)
Reviews (customerid, bookid, rating)
Pricing (bookid, format, price)

我有这个问题：

查找有关“CIVIL WAR”（即标题包含“CIVIL WAR”）的书籍的评分信息（显示标题、作者和平均评分）。

到目前为止，我得到的是：

SELECT title, author, AVG(r1.rating)
FROM Books, Reviews
WHERE title LIKE '%CIVIL WAR%'

但它是错误的:(任何帮助将不胜感激:D

4

2 回答 2

3

这遵循您提供的结构：

SELECT books.title, books.author, AVG(reviews.rating)
  FROM books, reviews
 WHERE books.bookid = reviews.bookid 
   AND books.title LIKE '%CIVIL WAR%'
GROUP BY books.title, books.author

您还可以考虑使用 a而不是像我那样JOIN在子句中进行 join ：WHERE

FROM books
JOIN reviews ON reviews.bookid = books.bookid

此外，请考虑为表使用别名，因为这将缩短更复杂的查询：

FROM `Books b` 

--Will enable you to write 
 AND b.title LIKE '%CIVIL WAR%'
于 2013-10-11T12:10:51.233 回答
2

尝试这个：

SELECT B.title, B.author, AVG(R.rating) Avg_Rating
FROM Books B
  JOIN Reviews R
   ON B.bookid = R.bookid
WHERE B.title LIKE '%CIVIL WAR%'
GROUP BY B.title, B.author

如果您有多个标题/作者，您也可以按 bookid 分组。

SELECT B.title, B.author, AVG(R.rating) Avg_Rating
FROM Books B
  JOIN Reviews R
   ON B.bookid = R.bookid
WHERE B.title LIKE '%CIVIL WAR%'
GROUP BY B.bookid, B.title, B.author
于 2013-10-11T12:12:49.887 回答