WITH daily AS (
  SELECT o.created_at::date AS day, sum(oi.quantity * oi.unit_price) AS revenue
  FROM orders o JOIN order_items oi ON oi.order_id = o.id
  WHERE o.status = 'done'
  GROUP BY day
)
SELECT day, revenue, sum(revenue) OVER (ORDER BY day) AS running
FROM daily
ORDER BY day
LIMIT 6;

SELECT id, customer_id, created_at,
  created_at - lag(created_at) OVER (PARTITION BY customer_id ORDER BY created_at) AS since_previous
FROM orders
WHERE customer_id = 1;

SELECT id, created_at::date AS day,
  count(*) OVER (ORDER BY created_at ROWS BETWEEN 2 PRECEDING AND CURRENT ROW) AS last3
FROM orders
LIMIT 5;