Write a SQL query to retrieve the revenue for the previous year.

Assuming a table sales with columns sale_date (DATE) and revenue (DECIMAL), you can get the previous calendar year’s revenue with:

SELECT SUM(revenue) AS total_revenue
FROM sales
WHERE YEAR(sale_date) = YEAR(CURRENT_DATE) - 1;

If you need the previous fiscal year or a rolling 12‑month period, adjust the date logic accordingly:

-- Rolling 12 months
SELECT SUM(revenue) AS total_revenue
FROM sales
WHERE sale_date >= DATE_SUB(CURRENT_DATE, INTERVAL 12 MONTH)
  AND sale_date < CURRENT_DATE;

Both queries run in O(n) time over the rows that satisfy the WHERE clause, and the index on sale_date (if present) will make the filtering efficient.