GROUP BY groups rows with same values into summary rows. Enables aggregates per group instead of entire table.

**GROUP BY Basics:**

- Groups rows by column values

- One result row per unique group

- Aggregates computed per group

- All non-aggregate columns must be in GROUP BY

**Execution Order:**

1. FROM: Get table

2. WHERE: Filter rows

3. GROUP BY: Group rows

4. Aggregates: Compute per group

5. HAVING: Filter groups

6. SELECT: Project columns

7. ORDER BY: Sort results

**NULL Handling:**

- NULL values form one group

- All NULLs grouped together

Foundation of analytics. Used in 90% of reporting queries. Understanding GROUP BY is critical for data analysts, BI developers, and backend engineers.

GROUP BY enables grouped analytics - sales by region, orders by customer, revenue by product category. Essential for every dashboard, report, and business intelligence query.