Have you optimized queries?

Query optimization starts with understanding the execution plan. I use EXPLAIN to see how the database accesses data, whether it uses indexes, and where scans occur. I create appropriate indexes on columns used in JOIN, WHERE, and ORDER BY clauses, but avoid over‑indexing to reduce write overhead. I enable statistics collection so the optimizer can choose efficient join orders. For complex queries, I break them into smaller steps, materialize intermediate results, or use common table expressions (CTEs) to improve readability. I also rewrite subqueries as joins when beneficial, and use EXISTS instead of IN for large sets. In OLAP contexts, I employ partition pruning and clustering keys. Finally, I monitor query performance over time, adjust indexes, and refactor slow queries based on real workloads.