使用mysql进行复杂的排序和分组

Question

我有ff表：

---------------------------
ID | ChapterNo | HitCount |  
---------------------------
1  |    2      |   1000   |
2  |    2      |   2000   |
3  |    1      |   3000   |
4  |    3      |   1000   |
5  |    1      |   3500   |
---------------------------

基本上我需要存档这个结果：

获取所有唯一的章节，每个章节的命中次数最多，然后以chapterno降序排序

ID | ChapterNo | HitCount |  
---------------------------
4  |    3      |   1000   |
2  |    2      |   2000   |
5  |    1      |   3500   |
---------------------------

我尝试了ff。查询：

SELECT t1.*, Max(t1.hitcount) AS maxhit
FROM chapter as t1
GROUP BY t1.chapterno
ORDER BY t1.chapterno DESC

但有些人如何不归还具有最高hitcount的那个。

我该如何解决这个问题？

谢谢

Answer 1

SELECT t1.*, t1.hitcount AS maxhit
FROM chapter as t1
WHERE t1.hitcount = (select max(hitcount) from chapter where chapterno = t1.chapterno)
ORDER BY t1.chapterno DESC

Answer 2

SELECT t1.id, t1.chapterno, t2.maxhits
FROM chapter as t1, 
    (SELECT id, chapterno, Max(hitcount) AS maxhits
     FROM chapter 
     GROUP BY chapterno) AS t2
WHERE t2.chapterno = t1.chapterno
AND t1.hitcount = t2.maxhits
ORDER BY t1.chapterno DESC

Answer 3

试试这个 -

SELECT c1.id, c1.ChapterNo, c1.HitCount FROM chapter c1
JOIN (SELECT ChapterNo, MAX(HitCount) max_hitCount
      FROM chapter
      GROUP BY ChapterNo) c2
ON c1.ChapterNo = c2.ChapterNo AND c1.HitCount = c2.max_hitCount
ORDER BY c1.ChapterNo DESC;

Answer 4

SELECT t1.*, t1.hitcount AS maxhit
FROM chapter as t1
WHERE t1.hitcount = (
    SELECT MAX t1.hitcount
    from chapter as t2
    where t2.ChapterNo = t1.chapterNo
)
ORDER BY t1.chapterno DESC

这使用相关的子查询，这可能变得无效。另一种可能性是在from或left join中使用不相关的查询。

More info on this article

Answer 5

虽然以上所有答案都很完美，但我认为也可以使用 SELF JOIN

完成

SELECT *
FROM chapter ch
WHERE (
   SELECT COUNT(*) FROM chapter ch2
   WHERE ch2.chapterno = ch.chapterno and ch2.hitcount > ch.hitcount
) <= 2;