SQL Window Functions vs GROUP BY: Key Differences Every Beginner Should Know

Both GROUP BY and window functions help summarize data in SQL, but they behave differently in how they return results. GROUP BY collapses multiple rows into a single summary row per group, losing individual row details in the process. Window functions, by contrast, retain every original row while adding a new calculated column alongside each one. Functions like AVG() with OVER/PARTITION BY, RANK(), and LAG() allow comparisons and rankings without reducing the dataset. Knowing which tool to use depends on whether you need a condensed summary or per-row calculations with context.