Your question is Optimize PostgreSQL Query Performance. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You are asked to improve slow SQL in a PostgreSQL database used for reporting and customer operations. The goal is to identify the main bottleneck and explain the steps you would take to make the workload faster without changing the business result.
Explain how you would approach database performance optimization in PostgreSQL. In your answer, cover how you would inspect the query plan, identify expensive joins or scans, decide when an index helps, and verify that the change actually improves runtime.
Keep your answer practical and structured. Focus on the sequence you would follow in a real investigation, including what you would check first, what evidence you would use, and how you would avoid common mistakes such as adding unnecessary indexes or optimizing the wrong query.