SQL: Find number of active "events" each month - sql

Question

Background
I have an SQL table that contains all events, with each event containing a unique identifier.
As you can see for some IDs the "event" stretches across multiple months. What I'm trying to find is the number of "active events" per month.
For example event ID:342, is active in both the month of Jan and Feb. So it should count towards both Jan and Feb's final count.
Example dataset
ID
Start Date
End Date
342
01 Jan 2022
12 Feb 2022
231
12 Feb 2022
26 Feb 2022
123
20 Jan 2022
10 Apr 2022
Desired output:
Month
Start Date
Jan
2
Feb
3
Mar
1
Apr
1
btw: I'm using Alibaba's ODPS SQL and not MySQL or Postgres. So i appreciate if the solution provided could be SQL system agnostic. Thanks!

Answer 1

Here is an example is MySQL 8, using a recursive CTE to construct the list of months. It would be more efficient to use a Calendar Table.
If you are not using MySQL you will need to modify the syntax of the query.
create table dataset(
ID int, Start_date Date,End_date Date);
insert into dataset values
(342,'2022-01-01','2022-02-12'),
(231,'2022-01-12','2022-02-26'),
(123,'2022-01-20','2022-04-10');
/*
Desired output:
Month Start Date
Jan 2
Feb 3
Mar 1
Apr 1
*/
✓
✓
✓
select
min(month(Start_date)),
max(month(End_date))
from dataset;
min(month(Start_date)) | max(month(End_date))
---------------------: | -------------------:
1 | 4
with recursive m as
(select min(month(Start_date)) mon from dataset
union all
select mon + 1 from m
where mon < (select max(month(End_date)) from dataset)
)
select
mon "month",
count(id) "Count"
from m
left join dataset
on month(Start_date)<= mon
and month(End_date) >= mon
group by mon
order by mon;
month | Count
----: | ----:
1 | 3
2 | 3
3 | 1
4 | 1
db<>fiddle here