What is the difference between HAVING and WHERE?

The main difference between HAVING and WHERE is the stage of data processing at which they are applied:

• WHERE filters rows before grouping. It is applied to the raw data and limits the set of rows that will be included in aggregate functions and grouping.

• HAVING filters groups after aggregate functions and grouping are performed. It is applied to the results of aggregation.

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 employees

Here, WHERE restricts the original rows, and HAVING filters the final groups.