Are you familiar with window functions? Can you explain any window function you have used in real time?

Window functions operate on a set of rows related to the current row, called a window, and return a single value for each row. Common examples include ROW_NUMBER(), RANK(), DENSE_RANK(), NTILE(), and LAG()/LEAD(). A real‑world use case is calculating a running total of sales per customer:

SELECT customer_id,
       order_date,
       amount,
       SUM(amount) OVER (PARTITION BY customer_id ORDER BY order_date
                         ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS running_total
FROM orders;

This query partitions the data by customer, orders each customer's orders chronologically, and sums amounts up to the current row, giving a cumulative total. Window functions are powerful for ranking, moving averages, and detecting gaps or duplicates without needing self‑joins or subqueries.