如何使用MySQL生成这两个报告？

Question

我的模式

我有以下表格

table             notes/example values
------------------------------------------------
users (
  id
  email           # "foo@example.com"
)                 

games (           
  id              
  name            # "Space Invaders", "Asteroids", "Centipede"
)                 

players (         
  id              
  name            # "uber dude"
  user_id         # player belongs to user
  game_id         # player belongs to game
)                 

scores (          
  id              
  player_id       # belongs to one player
  value           # 50
  created_at      # "2010-09-10",   "2010-08-05"
  month           # "2010-09",      "2010-08"
)

我需要创建两个报告。

1）顶级球员

在最近的四个月中，表现最好的球员（每个球员的所有分数）。每月显示前十名。

    2010-07         2010-08           2010-09    2010-10
 1  plyA 5,000 pts  plyB  9,400 pts   ...        ...
    Centipede       Solitaire

 2  plyB 3,600 pts  plyC  8,200 pts   ...        ...
    Asteroids       Centipede       

 3  plyC 2,900 pts  plyA  7,000 pts   ...        ...
    Centipede       Centipede

 4  ...             ...               ...        ...
 5  ...             ...               ...        ...
 6  ...             ...               ...        ...
 7  ...             ...               ...        ...
 8  ...             ...               ...        ...
 9  ...             ...               ...        ...
10  ...             ...               ...        ...

2）顶级用户：

在最近的4个月中，最佳性能用户（每个用户的每个玩家的所有分数）。每月显示前十名。

    2010-07           2010-08             2010-09    2010-10
 1  userA 50,000 pts  userB 51,400 pts    ...        ...
 2  userB 40,500 pts  userA 39,300 pts    ...        ...
 3  userC 40,200 pts  userC 37,000 pts    ...        ...
 4  ...               ...                 ...        ...
 5  ...               ...                 ...        ...
 6  ...               ...                 ...        ...
 7  ...               ...                 ...        ...
 8  ...               ...                 ...        ...
 9  ...               ...                 ...        ...
10  ...               ...                 ...        ...

MySQL视图助手

为了加入目的，我有一个存储的视图，可以帮助查询月份的月份。它将始终返回最近的四个月。

report_months (
  month
)

SELECT * FROM report_months;

2010-07
2010-08
2010-09
2010-10

问题

例如，在报告＃1中，我可以很容易地获得总和。

select
  p.name        as player_name,
  g.name        as game_name,
  s.month       as month,
  sum(s.score)  as sum_score

from players  as p

join games    as g
  on g.id = p.game_id

join scores   as s
  on s.player_id = p.id

join report_months as rm  -- handy view helper
  on rm.month = s.month

group by
  p.name, g.name

order by
  sum(s.score) desc

-- I can't do this :(
-- limit 0, 40

但是，我不能简单地获取前40个结果，并在4个月中散布它们，因为这不能保证我每个月的10个。

问题

我如何修改查询以确保我每月获得10次？

Answer 1

我不会尝试进行SQL查询，该查询像您所显示的那样按月制成。

相反，请查询每月排名前10的播放器作为行，而不是列：

Month    Rank  Player  TotalScore  Game
2010-07     1    plyA   5,000 pts  Centipede
2010-07     2    plyB   3,600 pts  Asteroids
2010-07     3    plyC   2,900 pts  Centipede
...
2010-08     1    plyB   9,400 pts  Solitaire
2010-08     2    plyC   8,200 pts  Centipede
2010-08     3    plyA   7,000 pts  Centipede
...

这变成了 greatest-n-per-group 问题，哪里 n 是10。

CREATE VIEW PlayerScoresByMonth AS
  SELECT month, player_id, SUM(value) AS score
  FROM scores
  GROUP BY month, player_id;

SELECT s1.month, COUNT(s2.month)+1 AS Rank, s1.player_id, s1.score AS TotalScore
FROM PlayerScoresByMonth s1
LEFT OUTER JOIN PlayerScoresByMonth s2 ON s1.month = s2.month 
  AND (s1.score < s2.score OR s1.score = s2.score AND s1.player_id < s2.player_id)
GROUP BY s1.month, s1.player_id
HAVING COUNT(*) < 10
ORDER BY s1.month, Rank;

（这是未经测试的，但应该让您开始）

然后，您需要编写一些应用程序代码来获取此查询的结果，并按月将列表分开，并提供数据，但您将要这样做。