0 需求描述
1 问题分析
目标：需要求出每个时间段，有客人在住的房间数量。
如果只考虑一人一房，我们可以借助于同时在线人数统计的思路，入住时间加辅助标记记为1，离店时间加辅助标记记为-1，并按照时间进行顺序排序，求当前累计值，具体SQL如下：
参考文章：SQL同时在线问题分析（求最高在线人数以及最高峰时间段）【累加器思想，流式分析】--HiveSql面试题29_sql统计同时在线时间_莫叫石榴姐的博客-CSDN博客
类似于公交车上车下车场景，统计公交车某一时刻车上人数，上车加1，下车减1，最终某一时刻人数通过加1减1这种辅助标记来进行累加，累加反应的是某一时间节点处，截止当前状态情况。
with data as
(
select 7 user_id, 2004 room_num, '2021-03-05' in_time, '2021-03-07' out_time
union all
select 23 user_id, 2010 room_num, '2021-03-05' in_time, '2021-03-06' out_time
union all
select 7 user_id, 1003 room_num, '2021-03-07' in_time, '2021-03-08' out_time
union all
select 8 user_id, 2014 room_num, '2021-03-07' in_time, '2021-03-08' out_time
union all
select 14 user_id, 3001 room_num, '2021-03-07' in_time, '2021-03-10' out_time
union all
select 18 user_id, 3002 room_num, '2021-03-08' in_time, '2021-03-10' out_time
union all
select 23 user_id, 3020 room_num, '2021-03-08' in_time, '2021-03-09' out_time
union all
select 25 user_id, 2006 room_num, '2021-03-09' in_time, '2021-03-12' out_time
)
select *
from (select time as start_time, lead(time) over (order by time) as end_time, acc_cnt
from (select time, sum(num) over (order by time) as acc_cnt
from (
select in_time as time, 1 as num
from data
union all
select out_time as time, -1 as num
from data
) t
) t
group by time, acc_cnt
) t
where end_time is not null 
但是这里面有个问题，实际场景是一人一房间吗？如果有多个人共住一房间，今天退了一个人，明天又退了一个人，后天的时候才退完，虽然在退，但房间还是有人住的，这种情况，是不是也算?如果考虑这种情况则需要对累加的状态进行调整，此时需要考虑每个房间中截止当前时间的人数情况。
第一步：先求出每个房间当前时间的人数累计值，作为状态判断辅助条件
增加一行数据：
union all
select 100 user_id,2004 room_num,'2021-03-05' in_time,'2021-03-08' out_time具体SQL如下：
with data as
(
select 7 user_id,2004 room_num,'2021-03-05' in_time,'2021-03-07' out_time
union all
select 23 user_id,2010 room_num,'2021-03-05' in_time,'2021-03-06' out_time
union all
select 7 user_id,1003 room_num,'2021-03-07' in_time,'2021-03-08' out_time
union all
select 8 user_id,2014 room_num,'2021-03-07' in_time,'2021-03-08' out_time
union all
select 14 user_id,3001 room_num,'2021-03-07' in_time,'2021-03-10' out_time
union all
select 18 user_id,3002 room_num,'2021-03-08' in_time,'2021-03-10' out_time
union all
select 23 user_id,3020 room_num,'2021-03-08' in_time,'2021-03-09' out_time
union all
select 25 user_id,2006 room_num,'2021-03-09' in_time,'2021-03-12' out_time
union all
select 100 user_id,2004 room_num,'2021-03-05' in_time,'2021-03-08' out_time
)
select time
, room_num
, sum(user_cnt) over (partition by room_num ORDER BY TIME) user_cnt
from (
select in_time as time, room_num, count(user_id) user_cnt
from data
group by in_time, room_num
union all
select out_time as time, room_num, -1 * count(user_id) user_cnt
from data
group by out_time, room_num
) t
第二步：基于累计的每个房间人数的状态变量进行判断：如果房间有人就标记1，没有人时候就标记为-1。标记思路实现：
方法1：case when 判断当user_cnt > 0时标记1，否则标记-1
case when user_cnt > 0 then 1 else -1 end num1方法2：判断每个房间截止当前人数的最小值，如果大于0 标记为1，否则标记为-1
case when min(user_cnt) over (partition by room_num order by time) > 0 then 1 else -1 end具体SQL如下：
with data as
(
select 7 user_id,2004 room_num,'2021-03-05' in_time,'2021-03-07' out_time
union all
select 23 user_id,2010 room_num,'2021-03-05' in_time,'2021-03-06' out_time
union all
select 7 user_id,1003 room_num,'2021-03-07' in_time,'2021-03-08' out_time
union all
select 8 user_id,2014 room_num,'2021-03-07' in_time,'2021-03-08' out_time
union all
select 14 user_id,3001 room_num,'2021-03-07' in_time,'2021-03-10' out_time
union all
select 18 user_id,3002 room_num,'2021-03-08' in_time,'2021-03-10' out_time
union all
select 23 user_id,3020 room_num,'2021-03-08' in_time,'2021-03-09' out_time
union all
select 25 user_id,2006 room_num,'2021-03-09' in_time,'2021-03-12' out_time
union all
select 100 user_id,2004 room_num,'2021-03-05' in_time,'2021-03-08' out_time
)
select time
, room_num
, user_cnt
, case when user_cnt > 0 then 1 else -1 end num1
, case when min(user_cnt) over (partition by room_num order by time) > 0 then 1 else -1 end num2
from (select time
, room_num
, sum(user_cnt) over (partition by room_num ORDER BY TIME) user_cnt
from (select in_time as time, room_num, count(user_id) user_cnt
from data
group by in_time, room_num
union all
select out_time as time, room_num, -1 * count(user_id) user_cnt
from data
group by out_time, room_num
) t
) t
第三步：
基于上述结果，累计num值（其实本质就是通过构造辅助条件对辅助标记值进行变换，累加值变了），反应截止当前时间点 有人入住的房间数量，最终SQL如下：
with data as
(
select 7 user_id,2004 room_num,'2021-03-05' in_time,'2021-03-07' out_time
union all
select 23 user_id,2010 room_num,'2021-03-05' in_time,'2021-03-06' out_time
union all
select 7 user_id,1003 room_num,'2021-03-07' in_time,'2021-03-08' out_time
union all
select 8 user_id,2014 room_num,'2021-03-07' in_time,'2021-03-08' out_time
union all
select 14 user_id,3001 room_num,'2021-03-07' in_time,'2021-03-10' out_time
union all
select 18 user_id,3002 room_num,'2021-03-08' in_time,'2021-03-10' out_time
union all
select 23 user_id,3020 room_num,'2021-03-08' in_time,'2021-03-09' out_time
union all
select 25 user_id,2006 room_num,'2021-03-09' in_time,'2021-03-12' out_time
-- union all
-- select 100 user_id,2004 room_num,'2021-03-05' in_time,'2021-03-08' out_time
)
select *
from
(select time as start_time, lead(time) over (order by time) as end_time, acc_cnt
from (select time
, sum(case when user_cnt > 0 then 1 else -1 end) over (order by time) acc_cnt
from (select time
, room_num
, sum(user_cnt) over (partition by room_num ORDER BY TIME) user_cnt
from (select in_time as time, room_num, count(user_id) user_cnt
from data
group by in_time, room_num
union all
select out_time as time, room_num, -1 * count(user_id) user_cnt
from data
group by out_time, room_num
) t
) t
) t
group by time, acc_cnt
) t
where end_time is not null最终结果如下：
新增测试数据结果如下：
with data as
(
select 7 user_id,2004 room_num,'2021-03-05' in_time,'2021-03-07' out_time
union all
select 23 user_id,2010 room_num,'2021-03-05' in_time,'2021-03-06' out_time
union all
select 7 user_id,1003 room_num,'2021-03-07' in_time,'2021-03-08' out_time
union all
select 8 user_id,2014 room_num,'2021-03-07' in_time,'2021-03-08' out_time
union all
select 14 user_id,3001 room_num,'2021-03-07' in_time,'2021-03-10' out_time
union all
select 18 user_id,3002 room_num,'2021-03-08' in_time,'2021-03-10' out_time
union all
select 23 user_id,3020 room_num,'2021-03-08' in_time,'2021-03-09' out_time
union all
select 25 user_id,2006 room_num,'2021-03-09' in_time,'2021-03-12' out_time
union all
select 100 user_id,2004 room_num,'2021-03-05' in_time,'2021-03-08' out_time
)
select *
from
(select time as start_time, lead(time) over (order by time) as end_time, acc_cnt
from (select time, sum(case when user_cnt > 0 then 1 else -1 end) over (order by time) acc_cnt
from (select time
, room_num
, sum(user_cnt) over (partition by room_num ORDER BY TIME) user_cnt
from (select in_time as time, room_num, count(user_id) user_cnt
from data
group by in_time, room_num
union all
select out_time as time, room_num, -1 * count(user_id) user_cnt
from data
group by out_time, room_num
) t
) t
) t
group by time, acc_cnt
) t
where end_time is not null
2 小结
本文总结了一种当前时间点状态统计的思路和方法，对于此类问题主要采用构造辅助计数变量及累加变换思路进行求解。常见的场景有：直播同时在线人数、服务器实时并发数、公家车当前时间段人数、某个仓库的货物积压数量，某一段时间内的同时处于服务过程中的最大订单量等