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Formatted question description: https://leetcode.ca/all/1194.html
1194. Tournament Winners
Table: Players
+-------------+-------+
| Column Name | Type |
+-------------+-------+
| player_id | int |
| group_id | int |
+-------------+-------+
player_id is the primary key of this table.
Each row of this table indicates the group of each player.
Table: Matches
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| match_id | int |
| first_player | int |
| second_player | int |
| first_score | int |
| second_score | int |
+---------------+---------+
match_id is the primary key of this table.
Each row is a record of a match, first_player and second_player contain the player_id of each match.
first_score and second_score contain the number of points of the first_player and second_player respectively.
You may assume that, in each match, players belongs to the same group.
The winner in each group is the player who scored the maximum total points within the group.
In the case of a tie, the lowest player_id wins.
Write an SQL query to find the winner in each group.
The query result format is in the following example:
Players table:
+-----------+------------+
| player_id | group_id |
+-----------+------------+
| 15 | 1 |
| 25 | 1 |
| 30 | 1 |
| 45 | 1 |
| 10 | 2 |
| 35 | 2 |
| 50 | 2 |
| 20 | 3 |
| 40 | 3 |
+-----------+------------+
Matches table:
+------------+--------------+---------------+-------------+--------------+
| 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 table:
+-----------+------------+
| group_id | player_id |
+-----------+------------+
| 1 | 15 |
| 2 | 35 |
| 3 | 40 |
+-----------+------------+
Algorithm
- step-1: get player-score table
- step-2: join to get group id, and order by max-score-first
- step-3: group by group
Code
SQL
select group_id, player_id from (
select p.group_id, ps.player_id, sum(ps.score) as score
from Players p,
(
select first_player as player_id, first_score as score
from Matches
union all
select second_player, second_score
from Matches
) ps
where p.player_id = ps.player_id
group by ps.player_id
order by group_id, score desc, player_id
-- limit 1 -- by default, groupby will pick the first one i.e. max score player here
) top_scores
group by group_id;