What is the difference between WHERE and HAVING in SQL?

**WHERE** filters rows BEFORE grouping
**HAVING** filters groups AFTER GROUP BY

```sql
-- WHERE: filter individual rows
SELECT * FROM employees WHERE salary > 50000;

-- HAVING: filter groups
SELECT department, AVG(salary) as avg_sal
FROM employees
GROUP BY department
HAVING AVG(salary) > 60000;
```

Simple rule: Use WHERE for rows, HAVING for aggregated groups.