Your question is Handling NULLs in Joins. 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).
In marketing analytics, especially when combining campaign activity from Veeva CRM and reference data from Veeva Vault, NULL values can quietly change join results and lead to missing or misleading rows.
Explain how you handle NULL values when performing a join in PostgreSQL. You should describe how NULL behaves in join conditions, how INNER JOIN and LEFT JOIN differ when join keys or joined columns contain NULLs, and when you would use COALESCE, IS NULL, or filtering logic after the join.
The interviewer is looking for a practical explanation, not just a definition. You should be able to explain common pitfalls, show how NULLs affect row retention, and give a few short SQL examples that demonstrate the right way to preserve unmatched rows or substitute default values in the result.