如何编写这个SQL语句？

Question

这是表: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,比如说,表格会是这样的:

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