1212，查询球队积分

查询球队积分

表: Teams

+---------------+----------+
| Column Name   | Type     |
+---------------+----------+
| team_id       | int      |
| team_name     | varchar  |
+---------------+----------+
team_id 是该表具有唯一值的列。
表中的每一行都代表一支独立足球队。

表: Matches

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| match_id      | int     |
| host_team     | int     |
| guest_team    | int     | 
| host_goals    | int     |
| guest_goals   | int     |
+---------------+---------+
match_id 是该表具有唯一值的列。
表中的每一行都代表一场已结束的比赛。
比赛的主客队分别由它们自己的 id 表示，他们的进球由 host_goals 和 guest_goals 分别表示。

你希望在所有比赛之后计算所有球队的比分。积分奖励方式如下:

如果球队赢了比赛(即比对手进更多的球)，就得 3 分。
如果双方打成平手(即，与对方得分相同)，则得 1 分。
如果球队输掉了比赛(例如，比对手少进球)，就 不得分 。

编写解决方案，以找出每个队的 team_id，team_name 和 num_points。

返回的结果根据 num_points 降序排序，如果有两队积分相同，那么这两队按 team_id 升序排序。

返回结果格式如下。

示例 1:

输入：
Teams table:
+-----------+--------------+
| team_id   | team_name    |
+-----------+--------------+
| 10        | Leetcode FC  |
| 20        | NewYork FC   |
| 30        | Atlanta FC   |
| 40        | Chicago FC   |
| 50        | Toronto FC   |
+-----------+--------------+
Matches table:
+------------+--------------+---------------+-------------+--------------+
| match_id   | host_team    | guest_team    | host_goals  | guest_goals  |
+------------+--------------+---------------+-------------+--------------+
| 1          | 10           | 20            | 3           | 0            |
| 2          | 30           | 10            | 2           | 2            |
| 3          | 10           | 50            | 5           | 1            |
| 4          | 20           | 30            | 1           | 0            |
| 5          | 50           | 30            | 1           | 0            |
+------------+--------------+---------------+-------------+--------------+
输出：
+------------+--------------+---------------+
| team_id    | team_name    | num_points    |
+------------+--------------+---------------+
| 10         | Leetcode FC  | 7             |
| 20         | NewYork FC   | 3             |
| 50         | Toronto FC   | 3             |
| 30         | Atlanta FC   | 1             |
| 40         | Chicago FC   | 0             |
+------------+--------------+---------------+

数据准备

drop database if exists db_1;
create database db_1;
use db_1;;

Create table If Not Exists Teams (team_id int, team_name varchar(30));
Create table If Not Exists Matches (match_id int, host_team int, guest_team int, host_goals int, guest_goals int);
Truncate table Teams;
insert into Teams (team_id, team_name) values ('10', 'Leetcode FC');
insert into Teams (team_id, team_name) values ('20', 'NewYork FC');
insert into Teams (team_id, team_name) values ('30', 'Atlanta FC');
insert into Teams (team_id, team_name) values ('40', 'Chicago FC');
insert into Teams (team_id, team_name) values ('50', 'Toronto FC');
Truncate table Matches;
insert into Matches (match_id, host_team, guest_team, host_goals, guest_goals) values ('1', '10', '20', '3', '0');
insert into Matches (match_id, host_team, guest_team, host_goals, guest_goals) values ('2', '30', '10', '2', '2');
insert into Matches (match_id, host_team, guest_team, host_goals, guest_goals) values ('3', '10', '50', '5', '1');
insert into Matches (match_id, host_team, guest_team, host_goals, guest_goals) values ('4', '20', '30', '1', '0');
insert into Matches (match_id, host_team, guest_team, host_goals, guest_goals) values ('5', '50', '30', '1', '0');

teams 表

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Matches 表

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分析 + 实现

第一步：计算每一个球队作为主队的得分

-- 计算每一个球队作为主队的得分
select
    host_team team_id,
    case
        when host_goals > guest_goals then 3
        when host_goals = guest_goals then 1
        else 0
    end as num_points
from matches;

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第二步：计算每一个球队作为客队的得分

-- 计算每一个球队作为客队的得分
select
    guest_team team_id,
    case
        when guest_goals > host_goals then 3
        when guest_goals = host_goals then 1
        else 0
    end as num_points
from matches;

在这里插入图片描述

第三步：组建临时表

-- 计算每一个球队作为主队的得分
select
    host_team team_id,
    case
        when host_goals > guest_goals then 3
        when host_goals = guest_goals then 1
        else 0
    end as num_points
from matches
union all
-- 计算每一个球队作为客队的得分
select
    guest_team team_id,
    case
        when guest_goals > host_goals then 3
        when guest_goals = host_goals then 1
        else 0
    end as num_points
from matches

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第四步：与 teams 表 进行左连接，查询每一个球队的分数

select
    *
from teams t
left join (
-- 计算每一个球队作为主队的得分
select
    host_team team_id,
    case
        when host_goals > guest_goals then 3
        when host_goals = guest_goals then 1
        else 0
    end as num_points
from matches
union all
-- 计算每一个球队作为客队的得分
select
    guest_team team_id,
    case
        when guest_goals > host_goals then 3
        when guest_goals = host_goals then 1
        else 0
    end as num_points
from matches
) points on t.team_id = points.team_id;

在这里插入图片描述

第五步：分组聚合，求总分并排序

select
    t.team_id,
    t.team_name,
    ifnull(sum(points.num_points), 0) as num_points
from teams t
left join (
-- 计算每一个球队作为主队的得分
select
    host_team team_id,
    case
        when host_goals > guest_goals then 3
        when host_goals = guest_goals then 1
        else 0
    end as num_points
from matches
union all
-- 计算每一个球队作为客队的得分
select
    guest_team team_id,
    case
        when guest_goals > host_goals then 3
        when guest_goals = host_goals then 1
        else 0
    end as num_points
from matches
) points on t.team_id = points.team_id
group by t.team_id, t.team_name
order by num_points desc, t.team_id;