C_R

WITH user_count AS (
SELECT
    orders.user_id,
    MIN (DATE_TRUNC('month', events.event_time)::date) AS start
FROM tools_shop.orders AS orders
INNER JOIN tools_shop.users AS users ON orders.user_id = users.user_id
INNER JOIN tools_shop.events AS events ON events.user_id = users.user_id
GROUP BY orders.user_id

)

SELECT
    user_count.start AS start,
    CAST( DATE_TRUNC('month', events.event_time) AS date) as month,
    COUNT(DISTINCT user_count.user_id)

FROM user_count INNER JOIN tools_shop.events AS events ON events.user_id = user_count.user_id
GROUP BY start, month