Question

我有这个SQL查询来获取租用某些类别书籍的次数。

SELECT Category.name, COUNT(*) AS "times rented"
FROM Category
INNER JOIN Book ON Book.category=Category.name
INNER JOIN Rent ON Rent.book_id=Book.id
GROUP BY Category.name
ORDER BY COUNT(*) DESC
LIMIT 1

如果我想获得最受欢迎的书，现在这将完美地运作。问题在于“限制1”。我有多本书，与上面的查询结果一样多次租用。删除“LIMIT 1”只会返回所有租借的类别。

假设上面的查询返回此

name | times rented
Adventure 153
Comics 153
Biography 102
Romance 80

如何同时返回“冒险”和“漫画”？

Answer 1

您可以使用MAX（）。

SELECT Category.name, COUNT(*) times_rented
FROM Category
INNER JOIN Book ON Book.category=Category.name
INNER JOIN Rent ON Rent.book_id=Book.id
INNER JOIN (select  MAX(COUNT(*)) max_count FROM Category GROUP BY Category.name) t ON t.id = Category.id AND Category.times_rented = t.max_count
GROUP BY Category.name

Answer 2

您可以使用最大计数进行比较，并将"替换为backticks中的times rented，将其用作别名而不发出警告。

SELECT Category.name, COUNT(*) AS `times rented`
FROM Category
INNER JOIN Book ON Book.category=Category.name
INNER JOIN Rent ON Rent.book_id=Book.id
GROUP BY Category.name
having  `times rented` = (select MAX(cnt) from 
(select COUNT(*) as cnt FROM Category GROUP BY Category.name) temp
)

表中的最高值

2 个答案: