Question

我试图从正在阅读的sql书中找出这个查询。

根据提供课程的次数查找最受欢迎课程的名称。

我有查询，如果它列出了课程，并计算每个提供了多少次，现在我的问题是如何满足上面的问题大声笑。我怎样才能获得最多提供的课程？（即数据库课程）

我的查询是

SELECT
    count(s.course_id) AS Times_Offered,
    c.title
FROM
    sections s
INNER JOIN courses c ON c.id = s.course_id
GROUP BY    c.title
ORDER BY    Times_Offered DESC;

我的查询显示为

times_offered   title
     3        Databases
     3        Calculus 1
     2        Compilers
     2        Elocution
     2        Acting
     1        Topology

Answer 1

如果你想要最受欢迎的课程，你需要获得所有最大的课程。这将给出你期望的答案。

SELECT 
count(s.course_id) AS Times_Offered,
c.title
FROM
sections s
INNER JOIN courses c ON c.id = s.course_id
GROUP BY    c.title
ORDER BY    Times_Offered DESC
Having Times_Offered =
SELECT max(t1.Times_offered) from
(SELECT 
count(s.course_id) AS Times_Offered,
c.title
FROM
sections s
INNER JOIN courses c ON c.id = s.course_id
GROUP BY    c.title
ORDER BY    Times_Offered DESC) t1

你的答案应该是

times_offered   title
 3        Databases
 3        Calculus 1

Answer 2

如果您想对它们进行计数，然后只显示编号最高的那个，请尝试：

SELECT COUNT(s.course_id) 
AS Times_Offered, c.title FROM sections s 
INNER JOIN courses c ON c.id=s.course_id 
GROUP BY c.title 
ORDER BY Times_Offered DESC
LIMIT 1

sql查询与count混淆

2 个答案: