LeetCode_sql_day24（1212.查询球队积分）

描述

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

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')

分析

法一：
①先计算出主队得分和客队得分情况

select host_team,guest_team,host_goals,guest_goals,casewhen host_goals > guest_goals then 3when host_goals = guest_goals then 1else 0 end host_points,casewhen host_goals < guest_goals then 3when host_goals = guest_goals then 1else 0 end guest_pointsfrom matches

②然后根据主队、客队得分情况求和

with t1 as (select host_team,guest_team,host_goals,guest_goals,casewhen host_goals > guest_goals then 3when host_goals = guest_goals then 1else 0 end host_points,casewhen host_goals < guest_goals then 3when host_goals = guest_goals then 1else 0 end guest_pointsfrom matches)select host_team, sum(host_points) points1from t1group by host_teamunion allselect guest_team, sum(guest_points) points1from t1group by guest_team

③连接两张表根据球队分组求总共的分数此处是用teams左连接获取到所有球队信息

用ifnull函数先对分数判空如果为空则赋0

select team_id, team_name, sum(ifnull(points1, 0)) num_points
from teamsleft join t2on teams.team_id = t2.host_team
group by team_id, team_name
order by num_points desc, team_id

法二：

①先连接两张表条件是 team_id = host_team or team_id = guest_team 并且为左连接

select team_id,team_name from Teams left join matches on team_id = host_team  or team_id = guest_team

②对各个球队得分进行定义

如果是根据主队id关联那么主队赢了积三分

如果是根据客队id关联那么客队赢了积三分

如果主队得分=客队那么不论根据什么关联都积一分

否则就是零分

select team_id,team_name ,casewhen team_id = host_team and host_goals > guest_goals then 3when host_goals = guest_goals then 1when team_id = guest_team and host_goals < guest_goals then 3else 0 end num_points
from Teams left join matches on team_id = host_team  or team_id = guest_team

③然后根据上一步结果进行分组排序

select team_id,team_name ,sum(casewhen team_id = host_team and host_goals > guest_goals then 3when host_goals = guest_goals then 1when team_id = guest_team and host_goals < guest_goals then 3else 0 end )num_points
from Teams left join matches on team_id = host_team  or team_id = guest_team
group by team_id, team_name
order by num_points desc,team_id

代码

# 法一
with t1 as (select host_team,guest_team,host_goals,guest_goals,casewhen host_goals > guest_goals then 3when host_goals = guest_goals then 1else 0 end host_points,casewhen host_goals < guest_goals then 3when host_goals = guest_goals then 1else 0 end guest_pointsfrom matches), t2 as (select host_team, sum(host_points) points1from t1group by host_teamunion allselect guest_team, sum(guest_points) points1from t1group by guest_team)
select team_id, team_name, sum(ifnull(points1, 0)) num_points
from teamsleft join t2on teams.team_id = t2.host_team
group by team_id, team_name
order by num_points desc, team_id;
# 法二
select team_id,team_name ,sum(casewhen team_id = host_team and host_goals > guest_goals then 3when host_goals = guest_goals then 1when team_id = guest_team and host_goals < guest_goals then 3else 0 end )num_points
from Teams left join matches on team_id = host_team  or team_id = guest_team
group by team_id, team_name
order by num_points desc,team_id