Reviewed by Aditya Kumar · Last reviewed 2026-03-24
SCD in ETL: Type 1—overwrite; Type 2—add row with history; Type 3—add column. Implement Type 2: compare incoming to current by natural key; if changed, close current (end_date), insert new. Use MERGE or incremental logic. Tools: dbt incremental, Spark MERGE, SSIS SCD transform....
SCD in ETL: Type 1—overwrite; Type 2—add row with history; Type 3—add column. Implement Type 2: compare incoming to current by natural key; if changed, close current (end_date), insert new. Use MERGE or incremental logic. Tools: dbt incremental, Spark MERGE, SSIS SCD transform. Key: surrogate key, effective/expiry dates, is_current flag. Why it matters: Design choices compound at scale—wrong approach can cause 100× overhead. Scalability trade-offs: Profile before optimizing; validate on sample then full. Cost implications: Suboptimal choices multiply at billion-row scale.
Red Flag: Generic textbook answers. Pro-Move: 'At scale we measured X, implemented Y, achieved Z%—validated and iterated.'
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