**Architectural Logic**: SCD0 (no history) to SCD3 (current + previous value) adds limited history without full Type 2 complexity. **Migration**: Add prev_value and effective_from columns; on update, shift current→previous before applying new value. **SQL**: `UPDATE dim SET...
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Architectural Logic: SCD0 (no history) to SCD3 (current + previous value) adds limited history without full Type 2 complexity. Migration: Add prev_value and effective_from columns; on update, shift current→previous before applying new value. SQL: UPDATE dim SET prev_value = current_value, current_value = new_value, updated_at = NOW() WHERE key = X. Or MERGE with equivalent logic. Why SCD3: Suits attributes with rare, important changes (e.g., customer tier); avoids Type 2 row explosion. Scalability: SCD3 is storage-efficient vs SCD2; limited to one prior value. Migration Strategy: Backfill prev_value from archive or set to current for first migration; establish effective dates for auditability. Trade-off: SCD3 is simpler than SCD2 but can't answer 'what was value at date X' for arbitrary history.
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Analyze My Answer — FreeAccording to DataEngPrep.tech, this is one of the most frequently asked SQL interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.