MySQL 8.0

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CREATE TABLE db_user
(
 user_id  int PRIMARY KEY,
 create_date TEXT,
 country_code TEXT
 );
 
INSERT INTO db_user (user_id, create_date, country_code)
    VALUES
     (1, '2019-01-01', 'US'),
     (2, '2020-02-01', 'US'),
     (3, '2021-01-01', 'US'),
     (4, '2021-02-01', 'TR'),
     (5, '2021-03-01', 'FR'),
     (6, '2021-06-01', 'FR'),
     (7, '2021-02-11', 'US'),
     (8, '2021-02-19', 'TR'),
     (9, '2021-01-10', 'US');
    
CREATE TABLE db_payment
(
 user_id  int,
 payment_amount double,
 pay_date TEXT
 ); 
     
INSERT INTO db_payment (user_id, payment_amount, pay_date)
    VALUES
     (1, 10, '2019-01-01'),
     (1, 10, '2019-02-01'),
     (1, 10, '2019-03-01'),
     (3, 10, '2021-01-01'),
     (3, 10, '2021-02-01'),
     (4, 10, '2021-02-01'),
     (4, 10, '2021-03-01');
     
SELECT * FROM db_user;
SELECT * FROM db_payment;

Records: 9  Duplicates: 0  Warnings: 0



Records: 7  Duplicates: 0  Warnings: 0




user_id
create_date
country_code


1
2019-01-01
US

2
2020-02-01
US

3
2021-01-01
US

4
2021-02-01
TR

5
2021-03-01
FR

6
2021-06-01
FR

7
2021-02-11
US

8
2021-02-19
TR

9
2021-01-10
US




user_id
payment_amount
pay_date


1
10
2019-01-01

1
10
2019-02-01

1
10
2019-03-01

3
10
2021-01-01

3
10
2021-02-01

4
10
2021-02-01

4
10
2021-03-01


-- users joined in Jan
SELECT *
FROM db_user
WHERE db_user.create_date BETWEEN '2021-01-01' AND '2021-01-31';


user_id
create_date
country_code


3
2021-01-01
US

9
2021-01-10
US


-- users joined in Jan and their payments in Feb
SELECT *
FROM db_user
LEFT JOIN db_payment ON db_payment.user_id = db_user.user_id
                    AND db_payment.pay_date BETWEEN '2021-02-01' AND '2021-02-28'
WHERE db_user.create_date BETWEEN '2021-01-01' AND '2021-01-31';


user_id
create_date
country_code
user_id
payment_amount
pay_date


3
2021-01-01
US
3
10
2021-02-01

9
2021-01-10
US
null
null
null


SELECT 100 * COUNT(DISTINCT db_payment.user_id) / COUNT(DISTINCT db_user.user_id) AS percent_active_in_Feb_from_joined_in_Jan
FROM db_user
LEFT JOIN db_payment ON db_payment.user_id = db_user.user_id
                    AND db_payment.pay_date BETWEEN '2021-02-01' AND '2021-02-28'
WHERE db_user.create_date BETWEEN '2021-01-01' AND '2021-01-31';


percent_active_in_Feb_from_joined_in_Jan


50.0000

user_id	create_date	country_code
1	2019-01-01	US
2	2020-02-01	US
3	2021-01-01	US
4	2021-02-01	TR
5	2021-03-01	FR
6	2021-06-01	FR
7	2021-02-11	US
8	2021-02-19	TR
9	2021-01-10	US

user_id	payment_amount	pay_date
1	10	2019-01-01
1	10	2019-02-01
1	10	2019-03-01
3	10	2021-01-01
3	10	2021-02-01
4	10	2021-02-01
4	10	2021-03-01