extract monthly data with distinct user per month

Question

Does the following code extract distinct data for each month. I mean a user_id can be only one time in a given month but be appear several time if it is not in the same month?

SELECT COUNT(DISTINCT user_id), EXTRACT (MONTH FROM created_at) MTH
FROM user_logins
WHERE created_at >= '2017-01-01' AND
created_at <= '2018-04-10' 
GROUP BY EXTRACT (MONTH FROM created_at)
ORDER BY MTH ASC

Answer 1

I think you also need to add Year

SELECT
  COUNT(DISTINCT user_id),
  EXTRACT(YEAR FROM created_at) Y,
  EXTRACT(MONTH FROM created_at) M
FROM user_logins
WHERE created_at >= '2017-01-01'
  AND created_at <= '2018-04-10' 
GROUP BY EXTRACT(YEAR FROM created_at),EXTRACT(MONTH FROM created_at)
ORDER BY Y,M

And as variant you can use to_char function

SELECT
  COUNT(DISTINCT user_id),
  to_char(created_at, 'YYYY-MM') YM
FROM user_logins
WHERE created_at >= '2017-01-01'
  AND created_at <= '2018-04-10' 
GROUP BY to_char(created_at, 'YYYY-MM')
ORDER BY YM