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Databasesmedium

Why can the optimizer choose a bad query plan and how do statistics help?

Tags
#optimizer#statistics#cardinality#performance
Back to categoryPractice quiz

Answer

The optimizer picks a plan based on estimated row counts (cardinality). If estimates are wrong (stale stats, skewed data, correlated columns), it can choose the wrong join order or algorithm. Updating statistics (e.g., ANALYZE) and using appropriate indexes helps the optimizer estimate better.

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