GROUP BY & HAVING Clause in SQL

The GROUP BY and HAVING clauses are used to group rows based on column values and filter those groups after aggregation. They are essential for summary reports and analytical queries.

🔹 GROUP BY

• Used to group rows that have the same values in specified columns.
• Often used with aggregate functions (COUNT, SUM, AVG, MIN, MAX).

SELECT department, COUNT(*) AS employee_count
FROM employees
GROUP BY department;

👉 Shows how many employees are in each department.

🔹 HAVING

• Works like WHERE, but is used after aggregation.
• Filters the groups created by GROUP BY.

SELECT department, COUNT(*) AS employee_count
FROM employees
GROUP BY department
HAVING COUNT(*) > 5;

👉 Shows only departments with more than 5 employees.

🔹 Key Differences (WHERE vs HAVING)

Feature	WHERE	HAVING
Filters rows	Before grouping	After grouping
Works with	Individual rows	Aggregate/grouped results
Example	WHERE salary > 50000	HAVING AVG(salary) > 60000