MySQL 限制用于计算 SUM 的行数

Question

我正在制作一款每小时计算玩家分数的游戏。需要分数，以便排行榜可以显示排名最高的玩家。 'points' 在游戏中获胜的玩家存储在 boards_played table 中。玩家 table 有一个分数字段，每小时更新一次 SQL:

update players p 
       inner join (
          SELECT player_id, sum(points) as total 
            from boards_played
           where time_played > DATE_SUB(now(), INTERVAL 7 DAY)
           GROUP BY player_id) s on p.player_id = s.player_id
  set p.score = s.total

问题是在 100 场比赛中获得 50 分的人应该比在 200 场比赛中获得 60 分的人排名更好。

简而言之，分数应该只基于你最近 7 天的最后 100 场比赛。

Answer 1

你可能需要一个相关的子查询，这样你就可以为每个玩家检索正确的值。

要找到某个玩家的总分，这个子查询就可以做到。

          SELECT SUM(points) as total
            FROM (
                   SELECT player_id, points
                     FROM boards_played
                    WHERE time_played > DATE_SUB(NOW(), INTERVAL 7 DAY)
                     AND player_id = ***something*** 
                    ORDER BY time_played DESC
                    LIMIT 100
                 ) a

现在，您需要将其合并到外部查询中

UPDATE players p
   SET score =
       (
          SELECT SUM(points) as total
            FROM (
                   SELECT points
                     FROM boards_played
                    WHERE time_played > DATE_SUB(NOW(), INTERVAL 7 DAY)
                      AND points.player_id = p.player_id 
                    ORDER BY time_played DESC
                    LIMIT 100
                 ) a
       )

为什么这叫做 相关？ 子查询 中的行 points.player_id = p.player_id 将它与外部查询相关。这样做可以让 LIMIT 分别应用于每个玩家的点数。

但是，你最好创建一个可以动态计算这个值的视图，而不是更新你的table。那么您就不必担心一直更新您的 table 了。它看起来像这样（未调试）。

CREATE VIEW players_with_score AS
SELECT p.player_id, p.col1, p.col2, p.col3,
       (  
          SELECT SUM(points) as total
            FROM (
                   SELECT points
                     FROM boards_played
                    WHERE time_played > DATE_SUB(NOW(), INTERVAL 7 DAY)
                      AND points.player_id = p.player_id 
                    ORDER BY time_played DESC
                    LIMIT 100
                 ) a
       ) score
  FROM player p

然后你可以这样说

  SELECT player_id, score
    FROM players_with_score
   WHERE score > 250

MySQL 限制用于计算 SUM 的行数

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