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#execution-engine

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01 ·Databases·FREE·10 min read Database Internals — What Happens Behind a Single Line of SQL Between hitting Enter on a SELECT and getting rows back, five stages run inside the database: parser, rewriter, planner, executor, storage. Here is why two plans returning identical rows can differ by orders of magnitude, and why stale statistics make a fast query go slow overnight — from zero background to the knobs you actually turn.