Writing Clean and Optimized SQL

Context

Teams rely on SQL that is easy to review, maintain, and run efficiently in production. Interviewers often use this question to test whether you can balance readability with performance instead of focusing only on syntax.

Core Question

Explain how you would write clean, optimized SQL in PostgreSQL. Your answer should cover:

1. How you structure queries so they are readable and maintainable
2. How you reduce unnecessary work in filters, aggregations, and sorting
3. How you think about correctness before optimization
4. How you validate that a query is actually efficient

Scope Guidance

Keep the discussion practical. The interviewer is not looking for obscure database internals, but they do expect you to mention query shape, selective filtering, choosing only needed columns, avoiding unnecessary complexity, and using tools like EXPLAIN to verify performance. A strong answer should connect code style with execution efficiency and mention common mistakes that make SQL harder to maintain or slower than necessary.