What is repeat purchase rate, and how do you measure it in Metabase?

Share of paying customers with more than one order.

-- Repeat purchase rate: share of customers with more than one paid order.
WITH per_customer AS (
  SELECT
    o.customer_id,
    COUNT(*) AS orders
  FROM orders o
  WHERE o.financial_status = 'paid'
  GROUP BY o.customer_id
)
SELECT
  COUNT(*)                                        AS customers,
  COUNT(*) FILTER (WHERE orders > 1)              AS repeat_customers,
  ROUND(100.0 * COUNT(*) FILTER (WHERE orders > 1)
        / NULLIF(COUNT(*), 0), 1)                 AS repeat_purchase_rate_pct
FROM per_customer;

Group customers by first-order month so maturity is comparable.

-- Repeat rate by first-order month (acquisition cohort).
WITH first_order AS (
  SELECT customer_id, MIN(created_at) AS first_at
  FROM orders WHERE financial_status = 'paid'
  GROUP BY customer_id
),
orders_per_customer AS (
  SELECT customer_id, COUNT(*) AS orders
  FROM orders WHERE financial_status = 'paid'
  GROUP BY customer_id
)
SELECT
  date_trunc('month', f.first_at)                 AS cohort_month,
  COUNT(*)                                        AS customers,
  ROUND(100.0 * COUNT(*) FILTER (WHERE o.orders > 1)
        / NULLIF(COUNT(*), 0), 1)                 AS repeat_rate_pct
FROM first_order f
JOIN orders_per_customer o ON o.customer_id = f.customer_id
GROUP BY date_trunc('month', f.first_at)
ORDER BY cohort_month;