Counting entries within time range in MySQL - mysql

Question

I have a table in my database where I am recording how long a user
is active or inactive. If a user switches from active to inactive or
vice versa (or changes any other attribute like address, etc) a new record is added. A simplified version looks like this:
UserID state state_from state_to
1 active 2016-12-14 2017-01-15
2 active 2016-12-14 2017-02-02
3 active 2017-01-01 NULL
1 inactive 2017-01-16 2017-03-05
2 inactive 2017-02-02 NULL
1 active 2017-03-06 NULL
I would like to count how many users had at some point the state "active", on a monthly basis. The desired output table for January till March would be:
date user_count
2017-01 3
2017-02 2
2017-03 2
For a specific timestamp (e.g. January 2017) I use the following query.
SET #stamp = '2017-01';
SELECT #stamp AS date, COUNT(UserID) AS user_count
FROM se_user
WHERE (state LIKE 'active' AND #stamp BETWEEN DATE_FORMAT(state_from,'%Y-%m') AND DATE_FORMAT(state_to,'%Y-%m') )
OR (state LIKE 'active' AND DATE_FORMAT(state_from,'%Y-%m') <= #stamp AND DATE_FORMAT(state_to,'%Y-%m') IS NULL);
My problem is, that I don't know how to do it for range of dates (say from January to March). Is there a way to do this?
Example database and table
-- Set up a test database
DROP DATABASE IF EXISTS se_toy_example;
CREATE DATABASE se_toy_example;
USE se_toy_example;
-- Create example table
DROP TABLE IF EXISTS se_user;
CREATE TABLE se_user (
UserID INT(10),
state VARCHAR(10),
state_from DATE,
state_to DATE
);
-- Populate table
INSERT INTO se_user (UserID,state,state_from,state_to)
VALUES (1,'active','2016-12-14','2017-01-15'),
(2,'active','2016-12-14','2017-02-02'),
(3,'active','2017-01-01',NULL),
(1,'inactive','2017-01-16','2017-03-05'),
(2,'inactive','2017-02-02',NULL),
(1,'active','2017-03-06',NULL);

Answer 1

You need a calendar_table to have the month date ranges, with dt_begin and dt_end for each month.
So your query for the current year become.
SQL DEMO
SELECT c.dt_begin, count(*)
FROM calendar_table c
JOIN se_user u
ON c.dt_begin <= COALESCE(u.state_to, curdate() )
AND c.dt_end >= u.state_from
WHERE dt_begin >= '2017-01-01'
AND dt_begin <= '2017-12-01'
AND state = 'active'
GROUP BY c.dt_begin
;
OUTPUT
NOTE: You can use LEFT JOIN if want the months with 0 activity.