Your question is Ensuring Integrity Across Data Sources. 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).
Teams often combine data from application databases, vendor feeds, and event logs into a single reporting layer. If the integration logic is weak, duplicates, missing matches, inconsistent formats, and incorrect aggregates can quickly make downstream analysis unreliable.
What techniques would you use to ensure data integrity when combining multiple data sources in SQL? In your answer, explain how you would validate join keys, handle duplicates, standardize data types and formats, manage NULLs, and verify that row counts and aggregates remain correct after combining data.
Keep the discussion practical and SQL-focused. The interviewer is not looking for a full data platform design; they want to hear the core checks, query patterns, and validation habits you would use before and after merging datasets in PostgreSQL.