SQL Query Optimization: Techniques That Actually Work

Slow queries are the most common database problem. Here are the optimization techniques I use that produce measurable results. Query optimization is where I spend most of my database tuning time. A poorly written query can be hundreds of times slower than an optimized one, even with perfect indexes. The techniques I describe here are the ones I have used to reduce query times from minutes to milliseconds in production systems. Start with EXPLAIN ANALYZE Before optimizing, I always run EXPLAIN ANALYZE to see what the database is actually doing. The execution plan reveals whether indexes are being used, what join strategies are chosen, and where time is spent. Optimizing without looking at the plan is guessing. EXPLAIN ANALYZE SELECT u.name, COUNT(o.id) AS order_count FROM users u LEFT JOIN orders o ON u.id = o.user_id WHERE u.created_at >= '2026-01-01' GROUP BY u.name; The plan shows whether the database uses a nested loop join or a hash join, whether it scans the users table or uses an index, and the actual time each step takes. I look for sequential scans on large tables, expensive sort operations, and nested loops with…