1. 题目

Players 玩家表

+-------------+-------+
| Column Name | Type  |
+-------------+-------+
| player_id   | int   |
| group_id    | int   |
+-------------+-------+
玩家 ID 是此表的主键。
此表的每一行表示每个玩家的组。

Matches 赛事表

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| match_id      | int     |
| first_player  | int     |
| second_player | int     | 
| first_score   | int     |
| second_score  | int     |
+---------------+---------+
match_id 是此表的主键。
每一行是一场比赛的记录，第一名和第二名球员包含每场比赛的球员 ID。
第一个玩家和第二个玩家的分数分别包含第一个玩家和第二个玩家的分数。
你可以假设，在每一场比赛中，球员都属于同一组。

每组的获胜者是在组内得分最高的选手。
如果平局，player_id 最小 的选手获胜。

编写一个 SQL 查询来查找每组中的获胜者。

查询结果格式如下所示

Players 表:
+-----------+------------+
| player_id | group_id   |
+-----------+------------+
| 15        | 1          |
| 25        | 1          |
| 30        | 1          |
| 45        | 1          |
| 10        | 2          |
| 35        | 2          |
| 50        | 2          |
| 20        | 3          |
| 40        | 3          |
+-----------+------------+Matches 表:
+------------+--------------+---------------+-------------+--------------+
| match_id   | first_player | second_player | first_score | second_score |
+------------+--------------+---------------+-------------+--------------+
| 1          | 15           | 45            | 3           | 0            |
| 2          | 30           | 25            | 1           | 2            |
| 3          | 30           | 15            | 2           | 0            |
| 4          | 40           | 20            | 5           | 2            |
| 5          | 35           | 50            | 1           | 1            |
+------------+--------------+---------------+-------------+--------------+Result 表:
+-----------+------------+
| group_id  | player_id  |
+-----------+------------+ 
| 1         | 15         |
| 2         | 35         |
| 3         | 40         |
+-----------+------------+

来源：力扣（LeetCode） 链接：https://leetcode-cn.com/problems/tournament-winners
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

2. 解题

• 先把分数加起来

select player_id, sum(score) total_score
from
((select first_player player_id, first_score scorefrom Matches)union all(select second_player, second_scorefrom Matches)
) t1
group by player_id

{"headers": ["player_id", "total_score"], 
"values": [[15, 3], [30, 3], [40, 5], [35, 1], [45, 0], [25, 2], [20, 2], [50, 1]]}

• 左连接获取 分组id
• 窗口函数获取 组内排名

select group_id, player_id,rank() over(partition by group_id order by total_score desc, player_id) rnk
from
(select group_id, t2.player_id, total_scorefrom Players p left join(select player_id, sum(score) total_scorefrom((select first_player player_id, first_score scorefrom Matches)union all(select second_player, second_scorefrom Matches)) t1group by player_id) t2using(player_id)
) t3

• 取出排名为1的

# Write your MySQL query statement belowselect group_id, player_id
from 
(select group_id, player_id,rank() over(partition by group_id order by total_score desc, player_id) rnkfrom(select group_id, t2.player_id, total_scorefrom Players p left join(select player_id, sum(score) total_scorefrom((select first_player player_id, first_score scorefrom Matches)union all(select second_player, second_scorefrom Matches)) t1group by player_id) t2using(player_id)) t3
) t
where rnk = 1

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