Interview Guides
Joins are central to most transformation work in PostgreSQL, especially when combining fact and dimension data for reporting, reconciliation, or downstream models in PwC data workflows.
Explain how you use joins effectively in complex data transformations. Your answer should cover how you choose between INNER JOIN, LEFT JOIN, and other join patterns; how you validate join keys and cardinality; how you prevent duplicated rows; and how you handle NULL values introduced by joins.
You should also describe how you would approach a transformation that combines transactional data with reference data, and what checks you would apply to make sure the output is accurate.
The interviewer is looking for a practical explanation rather than syntax memorization. Focus on join strategy, data quality risks, and how your choices affect correctness in a real transformation pipeline.
