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Explain Slowly Changing Dimensions (SCD) and its types

SQLeasy0.4 min readPremium

**Architectural Logic**: SCD tracks dimension attribute changes; type choice affects history and storage. **Type 1**: Overwrite; no history. **Type 2**: New row; effective dates; current flag; full history. **Type 3**: Previous value column; limited history. **Type 4**: History...

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Frequency
Low
Asked at 1 company
Category
487
questions in SQL
Difficulty Split
130E|271M|86H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
JIO

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This easy-level SQL question appears frequently in data engineering interviews at companies like JIO. While less common, it tests deeper understanding that distinguishes strong candidates.

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Expert Answer
81 words

Architectural Logic: SCD tracks dimension attribute changes; type choice affects history and storage. Type 1: Overwrite; no history. Type 2: New row; effective dates; current flag; full history. Type 3: Previous value column; limited history. Type 4: History table. Type 6: Hybrid (1+2+3). Most Common: Type 2 for customer, product dimensions. Implementation: MERGE or INSERT/UPDATE; change detection via hash. Scalability: Type 2 row growth; surrogate keys. Best Practice: Surrogate keys; effective_from, effective_to; current_flag; handle late arrivals; choose type by business requirement.

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According 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.

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