SQL Performance — indexing, EXPLAIN plans, query tuning

Indexing

• Composite indexes match your query predicates
• Avoid leading wildcard LIKEs
• Covering indexes reduce random I/O

EXPLAIN Plans

• Check rows examined and key used
• Detect full scans and filesorts
• Use ANALYZE to validate statistics

Tuning

• Shape queries to use indexes
• Denormalize selectively for hot paths
• Cache results at the right layer