Interview Guides
You are reviewing a workflow that joins several tables and returns more rows than expected. This usually means one or more joins are not one-to-one, or a filter is being applied after row multiplication.
Explain how you would troubleshoot the workflow and identify which join is introducing duplicates. Describe how you would verify join cardinality, spot many-to-many relationships, and distinguish true duplicates from repeated business keys.
Focus on the SQL reasoning you would use to isolate the problem, not on generic ETL advice. A strong answer should cover join keys, uniqueness checks, intermediate row counts, and how you would fix the issue without losing valid records.
