What are some query optimization techniques you can use in SQL databases?

Query optimization is the process of improving the performance of a SQL query by reducing the amount of work the database engine must do. Common techniques include: 1) Indexing – creating B‑tree or bitmap indexes on columns used in WHERE, JOIN, or ORDER BY clauses to speed up lookups. 2) Join order and type – choosing the most selective join first and using hash or merge joins when appropriate. 3) Statistics – keeping table and column statistics up to date so the optimizer can estimate cardinalities accurately. 4) Partition pruning – filtering partitions before scanning tables. 5) Query rewrite – using materialized views or common table expressions to avoid expensive subqueries. 6) Limiting result sets – using LIMIT, TOP, or pagination to avoid full table scans. 7) Avoiding functions on indexed columns – keeping predicates simple so indexes can be used. By applying these techniques, you can reduce I/O, CPU usage, and overall query latency.