SQL query optimization involves refining SQL queries to improve performance and reduce execution time. Techniques include using proper indexing, avoiding unnecessary joins, and selecting only the necessary columns rather than using SELECT *. Query execution plans should be analyzed to identify bottlenecks. Optimizing the use of WHERE clauses, reducing subqueries, and utilizing proper data types also enhance speed. Using aggregate functions efficiently, ensuring the database schema is well-designed, and leveraging database-specific optimization features can further accelerate query performance. The goal is to execute queries faster, thus improving the overall efficiency of database operations and resource usage.