SQL Query Optimization

Query optimization makes databases faster and more scalable.

Optimization techniques

• Indexing: Create indexes on frequently queried columns.
• Query rewriting: Simplify complex queries.
• Join optimization: Choose appropriate join types.
• Avoid SELECT *: Request only needed columns.
• Limit result sets: Use LIMIT/TOP/FETCH.
• Batch operations: Group INSERT/UPDATE statements.

Index strategies

• Primary key indexes (automatic).
• Covering indexes (include all query columns).
• Composite indexes (multiple columns).
• Avoid over-indexing (slows writes).

Query analysis

• EXPLAIN/EXPLAIN ANALYZE (show execution plan).
• Identify table scans (bad) vs index seeks (good).
• Check for N+1 query problems.
• Monitor slow query logs.

Common anti-patterns

• Implicit type conversions.
• Functions on indexed columns (breaks index).
• OR conditions (consider UNION).
• Subqueries (consider JOINs).

Caching strategies

• Result caching (Redis, Memcached).
• Query caching (MySQL query cache).
• Application-level caching.