What is the difference between WHERE and HAVING?

WHERE and HAVING are filtering conditions in SQL, but they are applied at different stages of data processing:

• WHERE filters rows before grouping. It is applied to the raw data and limits the set of rows that will be processed further.

• HAVING filters groups after aggregate functions and grouping (GROUP BY) are performed. It is used to restrict groups based on aggregate conditions.

Example:

SELECT department, COUNT(*) as employee_count
FROM employees
WHERE salary > 50000  -- filter employees with salary > 50000
GROUP BY department
HAVING COUNT(*) > 10     -- select departments with more than 10 such employees

Here, employees with a salary above 50000 are selected first (WHERE), then they are grouped by department, and only those groups with more than 10 employees are chosen (HAVING).