Subquery in FROM (derived table)

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A subquery in FROM is called a derived table or inline view. It runs first, producing a temporary result set (aliased as 'totals') that the outer query treats like a real table. The inner query sums orders per customer: Alice=400, Bob=50. The outer WHERE total > 100 keeps only Alice. This pattern is an alternative to CTEs (WITH clauses) and is useful when you need to filter on aggregate results.