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SQLBeginner#keys
SQLIntermediate#queries
What is the logical order of execution of a SELECT query?
FROM/JOIN → WHERE → GROUP BY → HAVING → SELECT → DISTINCT → ORDER BY → LIMIT. This is why a SELECT alias cannot be used in WHERE but can be used in ORDER BY.
Example
SELECT dept_id, COUNT(*) AS c FROM employees WHERE active = 1 GROUP BY dept_id HAVING COUNT(*) > 2 ORDER BY c DESC LIMIT 5;