DATABASES GUIDE
SQL Query Optimization for Backend Engineers
By the HireReadyAI team · 8 min read
A practical EXPLAIN-driven process plus app-layer fixes like caching and batching.
A simple process
Find the slow query → EXPLAIN it → check rows examined vs returned → add or adjust indexes → rewrite selective predicates → re-measure under load. Avoid optimizing queries that are not on the critical path.
Patterns that fix latency
- Select only needed columns
- Page results; avoid OFFSET on huge pages when possible
- Rewrite OR into UNION when it unlocks indexes
- Eliminate N+1 with joins or batched IN queries
App-layer co-fixes
Caching, denormalized read models, and async aggregation sometimes beat squeezing one more millisecond from SQL. Say that out loud in system design and senior interviews.