SQL GROUP BY

GROUP BY is used to group rows that share the same values in specified columns and apply aggregate functions to each group.

🔹 Basic Syntax

SELECT column1, aggregate_function(column2)
FROM table_name
GROUP BY column1;

🔹 Example: Group Employees by Department

SELECT department, COUNT(*) AS total_employees, AVG(salary) AS avg_salary
FROM employees
GROUP BY department;

This query groups employees by department and calculates:

• Total employees per department
• Average salary per department

🔹 Multiple Columns Grouping

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

Groups data by both department and job title.

🔹 Using GROUP BY with HAVING (Filter Groups)

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

Only shows departments with more than 5 employees.

🧠 Quick Recap

✅ Use GROUP BY to summarize data by categories