Data Grouping and Aggregation

Aggregate Functions

SELECT COUNT(*) FROM employees;
SELECT AVG(salary) FROM employees;
SELECT SUM(salary) FROM employees;
SELECT MIN(salary), MAX(salary) FROM employees;

GROUP BY

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

SELECT department, AVG(salary) as avg_salary
FROM employees
GROUP BY department;

HAVING Clause

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

Multiple Grouping

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

Common Patterns

-- Department statistics
SELECT department,
     COUNT(*) as total_employees,
     AVG(salary) as avg_salary,
     MIN(salary) as min_salary,
     MAX(salary) as max_salary
FROM employees
GROUP BY department
ORDER BY avg_salary DESC;