Running totals and moving averages with windows

-- PostgreSQL: running totals and rolling averages with window functions.
SELECT day,
       amount,
       SUM(amount) OVER (ORDER BY day) AS running_total,
       ROUND(AVG(amount) OVER (
         ORDER BY day
         ROWS BETWEEN 6 PRECEDING AND CURRENT ROW
       ), 2) AS avg_7_days
FROM daily_sales
ORDER BY day;

-- Multiple series: restart the window for each account.
SELECT account_id,
       day,
       SUM(amount) OVER (
         PARTITION BY account_id
         ORDER BY day
       ) AS account_running_total
FROM daily_sales
ORDER BY account_id, day;