HAVING clause

The HAVING clause is optional and eliminates group rows that do not satisfy a given condition. HAVING is similar to the WHERE clause, but WHERE occurs before the grouping, and HAVING occurs after.

This means that the WHERE clause places conditions on selected columns, whereas the HAVING clause places conditions on groups created by the GROUP BY clause.

Here's an example showing the position of the HAVING clause in a SELECT query:

SELECT column1, column2
FROM table1, table2
WHERE [ conditions ]
GROUP BY column1, column2
HAVING [ conditions ]
ORDER BY column1, column2

Basic HAVING clause example:

-- compute the average salary per department per job_title
-- filtering the result set only to include the departments and job titles with an average salary of at least $50,000
SELECT department, job_title, AVG(salary)
FROM employees
GROUP BY department, job_title
HAVING AVG(salary) >= 50000;

This query results in a table with columns for department, job title, and average salary. Each row represents the average salary for a unique combination of department and job title, and only those groups with an average salary of at least $50,000 are returned.