What basic SQL query optimization techniques do you use?

I use several basic SQL optimization techniques: 1) Ensure proper indexing on columns used in WHERE, JOIN, and ORDER BY clauses. 2) Avoid SELECT *; instead, list only needed columns to reduce I/O. 3) Use EXISTS instead of IN when checking for existence to improve performance. 4) Rewrite subqueries as JOINs when appropriate, as many engines optimize JOINs better. 5) Use table aliases to make queries clearer and sometimes help the optimizer. 6) Analyze query plans with EXPLAIN to identify full table scans or expensive joins. 7) Keep statistics up to date so the optimizer can make accurate cost estimates. 8) For large tables, consider partitioning or sharding if queries are range‑based. These practices help reduce execution time and resource consumption.