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Feb 6, 2017 · Databases
Why a Regex IN Subquery Breaks Oracle Index Scan – Lessons from a Failed Optimization
The article recounts a real‑world Oracle SQL case where a REGEXP_SUBSTR‑based IN subquery caused the optimizer to abandon an index range scan, explores why predicate pushdown fails with CONNECT BY recursion, documents attempted hints, rewrites, and the ultimate lessons for SQL performance tuning.
IN SubqueryOraclePredicate Pushdown
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