SQL Query Optimization Guide

SQL Query Optimization Guide The difference between a query that runs in 50ms and one that runs in 50 seconds is almost never hardware — it's the query plan. This guide teaches you to read execution plans like a pro, choose the right indexes without guessing, partition tables for scale, and recognize the 20 most common SQL anti-patterns that silently destroy performance. Covers PostgreSQL and MySQL with engine-specific examples and EXPLAIN output analysis. Key Features Execution plan reading guide for both EXPLAIN ANALYZE (PostgreSQL) and EXPLAIN FORMAT=JSON (MySQL) with annotated real-world examples Index strategy framework covering B-tree, hash, GIN, GiST, and partial indexes with decision criteria for each 20 SQL anti-patterns with measured performance impact, detection queries, and refactored solutions Table partitioning patterns for range, list, and hash partitioning with partition pruning verification techniques JOIN optimization techniques including join order hints, materialize