如何获取mysql中分组在一起的两列计数之间的比率（排行榜死亡/死亡比率）

我在pvp射击游戏中有一个排行榜，我想显示前20名玩家的杀/死比率（总杀数除以总死亡数）

我有一个记录杀戮的杀戮表，看起来像：

| killer_id | killed_id | date | 
| patrick   | jim       | 2021-03-01 |
| greyson   | jim       | 2021-03-02|
| jim       | patrick   | 2021-03-03|

SELECT COUNT(*) as total_kills 
FROM kills 
GROUP BY killer_id 
ORDER BY total_kills DESC 
LIMIT 20

SELECT COUNT(*) as total_deaths 
FROM kills 
GROUP BY killed_id 
ORDER BY total_deaths DESC 
LIMIT 20

我可以通过以下方式获得总的死亡人数：

| killer_id | killed_id | date | 
| patrick   | jim       | 2021-03-01 |
| greyson   | jim       | 2021-03-02|
| jim       | patrick   | 2021-03-03|

SELECT COUNT(*) as total_kills 
FROM kills 
GROUP BY killer_id 
ORDER BY total_kills DESC 
LIMIT 20

SELECT COUNT(*) as total_deaths 
FROM kills 
GROUP BY killed_id 
ORDER BY total_deaths DESC 
LIMIT 20

我可以通过这样做得到总死亡人数：

| killer_id | killed_id | date | 
| patrick   | jim       | 2021-03-01 |
| greyson   | jim       | 2021-03-02|
| jim       | patrick   | 2021-03-03|

SELECT COUNT(*) as total_kills 
FROM kills 
GROUP BY killer_id 
ORDER BY total_kills DESC 
LIMIT 20

SELECT COUNT(*) as total_deaths 
FROM kills 
GROUP BY killed_id 
ORDER BY total_deaths DESC 
LIMIT 20

但是，我似乎无法将查询分组，以便返回最佳比率列表。它看起来像：

| player_id | kill_death_ratio (total kills / total deaths) |
| patrick   | 2.1            |
| jim       | 1.0            |
| greyson   | .9            |

这在单个查询中是否可行？

使用此查询：

SELECT killer_id player_id FROM kills UNION SELECT killed_id FROM kills

让所有的球员都坐在桌上。
然后使用

LEFT

连接到您的查询：

SELECT p.player_id, 
       COALESCE(t1.total_kills, 0) / t2.total_deaths kill_death_ratio
FROM (SELECT killer_id player_id FROM kills UNION SELECT killed_id FROM kills) p
LEFT JOIN (
  SELECT killer_id, COUNT(*) total_kills 
  FROM kills 
  GROUP BY killer_id 
) t1 ON t1.killer_id = p.player_id  LEFT JOIN (
  SELECT killed_id, COUNT(*) total_deaths 
  FROM kills 
  GROUP BY killed_id 
) t2 ON t2.killed_id = p.player_id

SELECT player_id, SUM(killer) / SUM(killed) kill_death_ratio
FROM (
  SELECT killer_id player_id, 1 killer, 0 killed
  FROM kills
  UNION ALL
  SELECT killed_id, 0, 1
  FROM kills
) t
GROUP BY player_id

或者，没有您的疑问：

SELECT p.player_id, 
       COALESCE(t1.total_kills, 0) / t2.total_deaths kill_death_ratio
FROM (SELECT killer_id player_id FROM kills UNION SELECT killed_id FROM kills) p
LEFT JOIN (
  SELECT killer_id, COUNT(*) total_kills 
  FROM kills 
  GROUP BY killer_id 
) t1 ON t1.killer_id = p.player_id  LEFT JOIN (
  SELECT killed_id, COUNT(*) total_deaths 
  FROM kills 
  GROUP BY killed_id 
) t2 ON t2.killed_id = p.player_id

SELECT player_id, SUM(killer) / SUM(killed) kill_death_ratio
FROM (
  SELECT killer_id player_id, 1 killer, 0 killed
  FROM kills
  UNION ALL
  SELECT killed_id, 0, 1
  FROM kills
) t
GROUP BY player_id

请参阅。
结果（针对您的样本数据）：

玩家id 致死率 吉姆 0.5 帕特里克 1 格雷森 无效的

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某些玩家的总死亡人数可能为0。在这种情况下你希望得到什么结果？难以置信。非常感谢。我的kills表上有近300k行，所以运行大约需要10秒，所以看起来需要缓存结果或采用不同的方法，但我学到了一些东西。仅供参考，如果你从未死过，我希望这个比率仅仅是死亡人数，所以我使用COALESCE（）在返回null的情况下返回总和（killer）。