一、题目
有好友关系表t_friend，记录了user1_id,user2_id的好友关系对。现定义用户受欢迎程度=用户拥有的朋友总数/平台上的用户总数,请计算出每个用户的受欢迎程度。
代码语言：javascript
复制
+-----------+-----------+
| user1_id | user2_id |
+-----------+-----------+
| 1 | 2 |
| 1 | 3 |
| 1 | 4 |
| 1 | 5 |
| 2 | 3 |
| 2 | 4 |
| 3 | 4 |
| 4 | 5 |
| 5 | 6 |
| 5 | 7 |
| 7 | 8 |
| 9 | 10 |
+-----------+-----------+
二、分析
- 题目中数据user1_id,user2_id为互为好友关系，为关系对，即1与2是好友关系，则1-2,2-1记录只会存在一条，为方便计算，我们需要有两条记录。所以将user2_id与user1_id 互换，然后与原表进行union all;
- 对union all后的数据，按照user1_id分组，统计user2_id的个数，即user1_id 的好友数据,使用开窗计算出用户总数；
维度 | 评分 |
|---|---|
题目难度 | ⭐️⭐️⭐️ |
题目清晰度 | ⭐️⭐️⭐️⭐️⭐️ |
业务常见度 | ⭐️⭐️⭐️⭐️ |
三、SQL
1.user1_id,user2_id互换，然后进行union all。
执行SQL
代码语言：javascript
复制
select user1_id,
user2_id
from t_friend
union all
select user2_id,
user1_id
from t_friend
查询结果
代码语言：javascript
复制
+---------------+---------------+
| _u1.user1_id | _u1.user2_id |
+---------------+---------------+
| 1 | 2 |
| 2 | 1 |
| 1 | 3 |
| 3 | 1 |
| 1 | 4 |
| 4 | 1 |
| 1 | 5 |
| 5 | 1 |
| 2 | 3 |
| 3 | 2 |
| 2 | 4 |
| 4 | 2 |
| 3 | 4 |
| 4 | 3 |
| 4 | 5 |
| 5 | 4 |
| 5 | 6 |
| 6 | 5 |
| 5 | 7 |
| 7 | 5 |
| 7 | 8 |
| 8 | 7 |
| 9 | 10 |
| 10 | 9 |
+---------------+---------------+
2.计算每个用户的好友数,开窗计算出总用户数
执行SQL
代码语言：javascript
复制
with tmp as
(select user1_id,
user2_id
from t_friend
union all
select user2_id,
user1_id
from t_friend)
select user1_id,
count(user2_id) as friend_cnt,
count(distinct user1_id) over () as total_cnt
from tmp
group by user1_id
查询结果
代码语言：javascript
复制
+-----------+-------------+------------+
| user1_id | friend_cnt | total_cnt |
+-----------+-------------+------------+
| 10 | 1 | 10 |
| 9 | 1 | 10 |
| 8 | 1 | 10 |
| 7 | 2 | 10 |
| 6 | 1 | 10 |
| 5 | 4 | 10 |
| 4 | 4 | 10 |
| 3 | 3 | 10 |
| 2 | 3 | 10 |
| 1 | 4 | 10 |
+-----------+-------------+------------+
3.用户好友数除以总用户数计算最终结果
代码语言：javascript
复制
with tmp as (select user1_id, user2_id from t_friend union all select user2_id, user1_id from t_friend) select user1_id, count(user2_id) / count(distinct user1_id) over () res from tmp group by user1_id
查询结果
代码语言：javascript
复制
+-----------+------+
| user1_id | res |
+-----------+------+
| 10 | 0.1 |
| 9 | 0.1 |
| 8 | 0.1 |
| 7 | 0.2 |
| 6 | 0.1 |
| 5 | 0.4 |
| 4 | 0.4 |
| 3 | 0.3 |
| 2 | 0.3 |
| 1 | 0.4 |
+-----------+------+
四、建表语句和数据插入
代码语言：javascript
复制
--建表语句
CREATE TABLE t_friend(
user1_id bigint COMMENT '用户1ID',
user2_id bigint COMMENT '用户2ID'
) COMMENT '好友关系表'
ROW FORMAT DELIMITED FIELDS TERMINATED BY '\t'
;
-- 插入数据
insert into t_friend(user1_id,user2_id)
values
(1,2),
(1,3),
(1,4),
(1,5),
(2,3),
(2,4),
(3,4),
(4,5),
(5,6),
(5,7),
(7,8),
(9,10)