Explain when a CTE should be folded, materialized, or left to the optimizer based on reuse, pushdown, and expensive computation.
Readable SQL is only half the job. The plan still matters. Why developers overtrust CTEs CTEs are excellent for naming stages of logic. That readability win is real. The mistake is assuming that cleaner structure is always neutral for execution. It is not. A CTE can become an optimization boundary depending on how often it is referenced and whether the engine can safely fold it. The real tradeoff: reuse versus pushdown Materialization helps when you want to compute something once and reuse it. Folding helps when parent filters, joins, or limits should shrink the work earlier. The same CTE can…
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