大数据面试SQL038 用户连续登录所有断点日期

一、题目

现有用户登录记录表，已经按照用户日期进行去重处理。请查询出用户连续登录中出现断点的所有日期

+----------+-------------+
| user_id  | login_date  |
+----------+-------------+
| aaa      | 2023-12-01  |
| aaa      | 2023-12-02  |
| aaa      | 2023-12-04  |
| aaa      | 2023-12-08  |
| aaa      | 2023-12-10  |
| bbb      | 2023-12-01  |
| bbb      | 2023-12-03  |
| bbb      | 2023-12-04  |
| bbb      | 2023-12-07  |
| bbb      | 2023-12-08  |
| bbb      | 2023-12-09  |
+----------+-------------+

期望输出结果

+----------+-------------+
| user_id  | login_date  |
+----------+-------------+
| aaa      | 2023-12-03  |
| aaa      | 2023-12-05  |
| aaa      | 2023-12-06  |
| aaa      | 2023-12-07  |
| aaa      | 2023-12-09  |
| bbb      | 2023-12-02  |
| bbb      | 2023-12-05  |
| bbb      | 2023-12-06  |
| bbb      | 2023-12-10  |
+----------+-------------+

二、分析

本题看上去是一个连续登录问题，但是求完连续之后，也没啥意义。如果我们有一张每个用户每天登录的全量数据表，则求的是未出现在表中的记录。所以实际考察的是生成内容。

维度	评分
题目难度	⭐️⭐️⭐️⭐️
题目清晰度	⭐️⭐️⭐️⭐️
业务常见度	⭐️⭐️⭐️

三、SQL

1.先生成2023-12-01到2023-12-10的日期表

select date_add(to_date('2023-12-01'),add_day) as dates
from (select explode(sequence(0,9)) as add_day)t

查询结果

2.生成每个用户的2023-12-01到2023-12-10的记录表

with dates as
(
	select
		date_add(to_date('2023-12-01'),add_day) as dates
	from
		(
			select explode(sequence(0,9)) as add_day
		)t
),
t_user as
	(
		select
			user_id
		from t_login_38 
		group by user_id
	)
select
	user_id,
	dates
from t_user full outer join dates

查询结果

3.关联查询，查询出未登录的日期

with dates as
(
	select
		date_add(to_date('2023-12-01'),add_day) as dates
	from
		(
			select explode(sequence(0,9)) as add_day
		)t
),
t_user as
	(
		select
			user_id
		from t_login_38 
		group by user_id
	),
t_user_date as
	(
		select
			user_id,
			dates
		from t_user
		full outer join
		dates
	)
select
	t_user_date.user_id as user_id,
	t_user_date.dates as login_date 
from t_user_date
left join t_login_38 
on t_user_date.user_id = t_login_38.user_id 
and t_user_date.dates = t_login_38.login_date
where t_login_38.login_date is null

查询结果

四、建表语句和数据插入

--建表语句
create table t_login_38
(
user_id string COMMENT '用户ID',
login_date string COMMENT '登录日期'
) COMMENT '用户登录记录表'
stored as orc
;
--插入数据
insert into t_login_38(user_id,login_date)
values
('aaa','2023-12-01'),
('aaa','2023-12-02'),
('aaa','2023-12-04'),
('aaa','2023-12-08'),
('aaa','2023-12-10'),
('bbb','2023-12-01'),
('bbb','2023-12-03'),
('bbb','2023-12-04'),
('bbb','2023-12-07'),
('bbb','2023-12-08'),
('bbb','2023-12-09')