SQL 跨表聚合列比率

Question

我正在为我正在制作的一款游戏制作一组排行榜，并希望能够在其中拥有一个“K/D”（杀戮-死亡比率）排行榜。即选择（总击杀数）/（总击杀数）比率最高的玩家。

我的数据库目前被格式化为有两个表，一个 Kill 表和一个 Death 表（我知道在这个例子中，将它们作为两个单独的表看起来很愚蠢，但是还有其他与问题无关的细节手头，所以这些需要单独的表）

杀表：

id	player_id	weapon_type	kill_count
1	1	Pistol	5
2	1	Rifle	10
3	2	Rifle	20
4	2	Pistol	7

死亡表：

id	player_id	weapon_type	death_count
1	1	Pistol	2
2	1	Rifle	20
3	2	Rifle	10
4	2	Pistol	3

（请参阅https://i.imgur.com/V8OEVxo.png 了解表格应该是什么样子，因为上面的格式搞砸了。）

根据上述数据，查询最高 K/D 比率将返回 (2,27/13), (1, 15/22)；即所有 (player_id, K/D ratio) 对按 K/D 比降序排列。

我已经为最高总击杀数等设置了其他排行榜，我实施如下：

SELECT player_id, sum(kill_count) as totalkills from Kill group by player_id order by totalkills desc;

这似乎工作正常，所以我认为我可以使用以下方法获得最高的 K/D 比率：

SELECT Kill.player_id, sum(kill_count)/sum(death_count) as KD from Kill, Death group by Kill.player_id order by KD desc;

但它给出了完全虚假的结果。

任何关于格式化我的查询的正确方法的指针将不胜感激:)

编辑：我不确定为什么表格在问题中的格式不正确，因为它们在预览中看起来不错。这是一个错误吗？

Answer 1

您好，我不明白您的问题。 我认为更好的方法是使用 Window Funktion。

Select player_id, Weapon_type, count() over (partition by player_id) as „killes pro player“ count() over (Partition by player_id, Weapon_type) „kills by player and weapon” from order通过 player_id;

Answer 2

您可以按玩家将击杀数和死亡数组合在一起，然后将它们组合起来以找到您要查找的内容：

WITH total_kills AS (
    SELECT player_id, sum(kill_count) as kill_count 
    FROM kill 
    GROUP BY player_id
), 
total_deaths AS (
    SELECT player_id, sum(death_count) as death_count 
    FROM death
    GROUP BY player_id
) 
SELECT total_kills.player_id, 1.0 * kill_count / NULLIF(death_count, 0) as kd
FROM total_kills, total_deaths 
WHERE total_kills.player_id = total_deaths.player_id
ORDER BY 2 DESC;

或者如果您更喜欢子查询：

SELECT total_kills.player_id, 1.0 * kill_count / NULLIF(death_count, 0) as kd
FROM 
    (SELECT player_id, sum(kill_count) as kill_count 
     FROM kill 
     GROUP BY player_id) as total_kills, 
    (SELECT player_id, sum(death_count) as death_count
     FROM death 
     GROUP BY player_id) as total_deaths 
WHERE total_kills.player_id = total_deaths.player_id
ORDER BY 2 DESC;

NULLIF 只是为了防止在玩家没有死亡时查询中断。