Window Functions

Use SQL Window Functions Without Losing Row Detail

Many SQL problems ask for a calculation across several rows while still returning each original row. For example, you may need to show every order together with the customer’s running spend, rank products inside each category, or compare today’s measurement with the previous one. A regular aggregate such as SUM() or AVG() can calculate across rows, but a GROUP BY query usually collapses those rows into one result row per group.