SQL Window Functions vs. Aggregate Functions: Key Differences Explained

SQL aggregate functions like SUM() and COUNT() collapse multiple rows into a single summary row per group, causing individual row details to be lost. Window functions perform similar calculations but retain all original rows, attaching computed results to each one using the OVER() clause. Unlike aggregate functions, window functions support ranking operations such as RANK() and DENSE_RANK(), enabling per-group rankings without complex subqueries or self-joins. Adding an ORDER BY clause inside OVER() further allows running totals and cumulative sums, a capability aggregate functions cannot replicate. The core distinction is that aggregate functions summarize data while window functions annotate it, making the latter more flexible for analytical queries.