HAVING vs WHERE with subqueries

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SQL processes clauses in this order: FROM -> WHERE -> GROUP BY -> HAVING -> SELECT -> ORDER BY. WHERE filters individual rows before any grouping happens, so it cannot see per-group aggregates like SUM(amount). HAVING filters after grouping, which is exactly where you need to compare a group's total against a threshold. A subquery in HAVING is the clean solution: HAVING SUM(amount) > (SELECT AVG(total) FROM ...). The subquery runs once and returns the threshold.