SQL for Product Managers
Data Quality and Trust
16. How do you sanity-check a number before presenting it to leadership?
Look for a concrete checklist, order of magnitude, denominator clarity, cross-checking against a known figure, not just "I double check it."
17. Describe a time (real or hypothetical) where a query returned a technically correct but practically misleading number. What caused it?
Tests real understanding of fan-out, wrong join types, or timezone issues, ideally with a specific, plausible example.
18. What does "grain" mean in the context of a data table, and why does it matter?
Tests whether the candidate understands that getting the grain wrong is a root cause of double-counting and inflated totals.
19. How would you explain to an engineer why a metric definition matters as much as the query itself?
Look for the idea that a technically correct query against a poorly defined metric still produces a number nobody should trust.
20. What's the difference between the data in a production database and the data in a data warehouse, and why does it matter for a PM?
Tests awareness of data freshness and pipeline lag, and the risk of treating a warehouse number as perfectly real-time.