Context

Slow SQL queries affect dashboards, reports, and application response times. Interviewers ask this question to see whether you can diagnose performance issues methodically instead of guessing.

Question

Explain how you would optimize a SQL query that is running slowly in PostgreSQL. Your answer should cover:

1. How you would identify the real bottleneck
2. What parts of the query and schema you would inspect first
3. How indexing, filtering, and aggregation patterns affect performance
4. How you would validate that your changes actually improved the query

Scope Guidance

Keep the answer practical and structured. The interviewer is not looking for deep PostgreSQL internals, but they do expect a clear workflow: inspect the execution plan, reduce unnecessary work, check indexes, and confirm improvements with measurement.