Reviewed by Aditya Kumar · Last reviewed 2026-03-24
Self-join for salary comparison: SELECT e1.name, e1.salary, e2.name AS higher_sal_name, e2.salary FROM emp e1 JOIN emp e2 ON e1.salary < e2.salary. To find employees with no one earning more in same dept: SELECT * FROM emp e1 WHERE NOT EXISTS (SELECT 1 FROM emp e2 WHERE e2.dept...
Self-join for salary comparison: SELECT e1.name, e1.salary, e2.name AS higher_sal_name, e2.salary FROM emp e1 JOIN emp e2 ON e1.salary < e2.salary. To find employees with no one earning more in same dept: SELECT * FROM emp e1 WHERE NOT EXISTS (SELECT 1 FROM emp e2 WHERE e2.dept = e1.dept AND e2.salary > e1.salary). Or use MAX with GROUP BY. Why it matters: Design choices compound at scale—wrong approach can cause 100× overhead. Scalability trade-offs: Profile before optimizing; validate on sample then full. Cost implications: Suboptimal choices multiply at billion-row scale.
Red Flag: Generic textbook answers. Pro-Move: 'At scale we measured X, implemented Y, achieved Z%—validated and iterated.'
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