MySQL GROUP BY Clause Explained with Examples

GROUP BY is the heart of data analysis in SQL. It collapses rows into groups so you can compute totals, averages, and counts per category — the exact logic behind every summary report and dashboard tile.

Key Points

• Basic pattern: SELECT department, COUNT(*) FROM employees GROUP BY department;
• Combine with aggregates: SUM(sales), AVG(salary), MAX(order_date)
• Filter groups with HAVING: HAVING COUNT(*) > 5
• Every non-aggregated column in SELECT must appear in GROUP BY
• Group by multiple columns for cross-tab style summaries
• WITH ROLLUP adds grand totals in one query