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，得分最低的选手获胜。

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         |
+-----------+------------+

先通过一次关联查询把每组每个player的总分查出来，再通过一次查询得到每组得分最高的，得分一样的取id最小的

select group_id,player_id from
(select group_id,player_id,sum((
case when player_id = first_player then first_score
when player_id = second_player then second_score
end
)) as totalScores
from Players p,Matches m
where p.player_id = m.first_player
or p.player_id = m.second_player
group by group_id,player_id
order by group_id,totalScores desc,player_id) as temp
group by group_id
order by group_id,totalScores desc,player_id

作者：couchpotato613
链接：https://leetcode-cn.com/problems/tournament-winners/solution/guan-lian-cha-xun-jia-shang-fen-zu-pai-xu-by-couch/
来源：力扣（LeetCode）
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