MySQL - Request to count periodically with accumulation - mysql

Question

Sorry if this is a duplicate but I never found an answer to this.
I have a User table which is as follows :
| id | pseudo | inscription date |
|----|-------------|------------------|
| 1 | johndoe | 01/01/1970 |
| 2 | janeyes | 02/01/1970 |
| 3 | thirdpseudo | 05/01/1970 |
And I am searching for a query to do statistics of accumulation. I would like to retrieve, day by day, the number of users registered.
I made a query that retrieves only for the registering days, but I don't find how to accumulate every days...
SELECT DATE_FORMAT(date, "%d/%m/%Y") AS 'Day', COUNT(*) AS 'Number of registered users'
FROM User
GROUP BY DATE(date)
ORDER BY date DESC;
This query outputs :
| date | number of registered users |
| ---------- | -------------------------- |
| 01/01/1970 | 1 |
| 02/01/1970 | 1 |
| 05/01/1970 | 1 |
The output I would like for this example is :
| date | number of registered users |
| ---------- | -------------------------- |
| 01/01/1970 | 1 |
| 02/01/1970 | 2 |
| 03/01/1970 | 2 |
| 04/01/1970 | 2 |
| 05/01/1970 | 3 |
| 06/01/1970 | 3 |

Answer 1

I would suggest to generate some dates data defined as range of dates. Then join all users available to these dates and count how many users were registered during such days.
Here is the code:
-- creating simple table
create table Users
(
id int not null,
pseudo varchar(15),
date date
);
-- adding some data
insert into Users
values
(1,'jonh','1970-01-01'),
(2,'doe','1970-01-02'),
(3,'janeyes','1970-01-02'),
(4,'third','1970-01-03'),
(5,'pseudo','1970-01-03'),
(6,'title','1970-01-04'),
(7,'somename','1970-01-04'),
(8,'anothername','1970-01-04');
-- defines the start date and the end date
set #startDate = '1970-01-01';
set #endDate = '1970-02-01';
-- recursively geneterates all dates within the range
with RECURSIVE dateRange (Date) as
(
select #startDate as Date
union ALL
select DATE_ADD(Date, INTERVAL 1 DAY)
from dateRange
where Date < #endDate
)
-- using SUM() over () would result in running total starting
-- from 1, it would count next day + all previous days
select Date, Sum(RegisteredUsersCount) over(order by RegisteredUsersCount asc
rows between unbounded preceding and current row) as RegisteredUsersCount
from
(
-- left join will join all users, if there is no users that correspond to the date of join, then it would be 0 for that date.
select dr.Date, Count(u.id) as RegisteredUsersCount
from dateRange as dr
left join Users as u
on dr.Date = u.date
group by dr.Date
) as t
order by Date asc;
And working example to test: SQLize Online