Question

这是表格：用户

Name:  Subject:
Peter   Math
Mary    Chinese
Mary    Computer
Mary    Hist
Mary    PE
Mary    English
Peter   Art
Chris   English
Chris   Computer
Peter   Computer
Paul    Math

我希望顶部出现在名称中，并返回前4个结果应该是主题名称。例如，在这种情况下，top出现名称是Mary，并且基于主题，中文，计算机，英语的顺序，所以我希望得到结果：

Mary    Chinese
Mary    Computer
Mary    English
Mary    Hist

如果Mary不是最能显示结果，那么第二个人就会跟随，就像，表格会这样：

Name:  Subject:
Peter   Math
Mary    Chinese
Mary    Computer
Mary    Hist
Peter   Art
Chris   English
Chris   Computer
Peter   Computer
Paul    Math

结果将是，

Mary    Chinese
Mary    Computer
Mary    Hist
Peter   Art

因为玛丽是最出现的，所以玛丽会回来，但玛丽不足以填补4个位置，所以第二个出现的位置将取代，在这种情况下，我们使用彼得。

Answer 1

SELECT user.name, user.subject
FROM user
INNER JOIN (
    SELECT name, COUNT(1) AS occurrences
    FROM user
    GROUP BY name
  ) AS user_occurrences
  ON user.name = user_occurrences.name
ORDER BY user_occurrences.occurrences DESC, user.name ASC, user.subject ASC
LIMIT 4

编辑这可能会更好，具体取决于您使用的RDBMS和数据集的大小。尝试两者并进行比较。

SELECT user.name, user.subject
FROM user
INNER JOIN user AS user_occurrences
  ON user.name = user_occurrences.name
GROUP BY user.name --, user.subject Second GROUP BY not needed on MySQL, but it should logically be there
ORDER BY COUNT(user_occurrences.subject) DESC, user.name ASC, user.subject ASC
LIMIT 4

Answer 2

按名称，主题和按计数排序

从组中选择前4名

MSSQL代码：

select top 4 q.marketname, cc.countryname from (
select top 100  m.MarketName, m.MarketId, COUNT(m.marketname) as [count]  
from Common.Country c inner join Common.Market m on c.MarketId = m.MarketId
group by m.MarketName, m.MarketId order by COUNT(m.marketname) desc) 
q inner join Common.Country cc
on cc.MarketId = q.MarketId order by [Count] desc

您可以制作类似的mySQL代码

这是相关的MySQL代码

select q.name, cc.subject from (
  select m.Name, count(*) as Count
  from User m
  group by m.Name 
  order by COUNT(*) desc 
  LIMIT 100
) q 
inner join user cc on cc.Name= q.name 
order by Count desc 
LIMIT 4

这是经过深思熟虑的，你想要解决方案吗？你不能在你的技术中实现逻辑吗？如果不了解建议的解决方案，就不应该进行投票。

如何编写这个SQL语句？

2 个答案: