Доля клиентов с покупками в нескольких месяцах

SQL, по которому посчитано

WITH bounds AS (
  SELECT date_trunc('month', max(date)) AS last_month
  FROM deals
),
months AS (
  SELECT t.month_start
  FROM generate_series(
    (SELECT last_month FROM bounds) - INTERVAL '11 months',
    (SELECT last_month FROM bounds),
    INTERVAL '1 month'
  ) AS t(month_start)
),
valid_deals AS (
  SELECT customer_id, date_trunc('month', date) AS month_start
  FROM deals
  WHERE status = 'Выиграна'
    AND customer_id IS NOT NULL
    AND customer_id <> ''
    AND date >= (SELECT last_month FROM bounds) - INTERVAL '11 months'
    AND date < (SELECT last_month FROM bounds) + INTERVAL '1 month'
),
customer_totals AS (
  SELECT customer_id, count(DISTINCT month_start) AS months_bought
  FROM valid_deals
  GROUP BY customer_id
),
monthly_customers AS (
  SELECT DISTINCT month_start, customer_id
  FROM valid_deals
)
SELECT
  m.month_start AS month_start,
  count(DISTINCT mc.customer_id) AS customers,
  count(DISTINCT CASE WHEN ct.months_bought > 1 THEN mc.customer_id END) AS multi_month_customers,
  round(
    1.0 * count(DISTINCT CASE WHEN ct.months_bought > 1 THEN mc.customer_id END)
    / nullif(count(DISTINCT mc.customer_id), 0),
    4
  ) AS multi_month_share
FROM months m
LEFT JOIN monthly_customers mc ON mc.month_start = m.month_start
LEFT JOIN customer_totals ct ON ct.customer_id = mc.customer_id
GROUP BY m.month_start
ORDER BY m.month_start