You are helping a client reconcile two Castlight reports that contain similar business data but are structured differently. The key is to explain whether they need to match rows side-by-side or stack rows into one combined set.
Explain the difference between a join and a union in SQL, and how you would choose between them when comparing two reports. In your answer, describe what each operation does to the row set, how column alignment works, and what happens when one report has rows that the other does not.
Keep the explanation practical and focused on reconciliation. The interviewer expects you to clarify when a join helps identify matched vs unmatched records, and when a union helps combine like-for-like rows from two sources into a single report.
