Context

Reporting datasets often fail because filtering rules are applied inconsistently across source rows, aggregated outputs, and downstream dashboards. Interviewers ask this to see whether you can separate business logic from SQL mechanics and build reliable, reusable datasets.

Question

Explain how you would handle filtering logic when building a reporting dataset in SQL. Your answer should cover:

1. Where filters should be applied in the query flow
2. The difference between row-level filtering and post-aggregation filtering
3. How to make filtering logic clear, reusable, and less error-prone
4. Common mistakes that lead to incorrect reporting results

Scope Guidance

Keep the discussion practical. The interviewer is looking for a structured explanation of how to design filtering logic for reporting, not just a definition of WHERE and HAVING.