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Home/Questions/SQL/Explain Data Modeling SCD Types (Type 1, 2, 3).

Explain Data Modeling SCD Types (Type 1, 2, 3).

SQLmedium0.5 min read

**Architectural Logic**: SCD types trade history depth vs storage and complexity. **Type 1**: Overwrite; no history. Use when history irrelevant (typo correction). **Type 2**: Full history; new row on change; effective_from, effective_to, current_flag. Use when history needed...

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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
EY
Key Concepts Tested
join

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This medium-level SQL question appears frequently in data engineering interviews at companies like EY. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (join) will help you answer variations of this question confidently.

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Break this problem into components. Identify the core trade-offs involved, then walk the interviewer through your reasoning step by step. Demonstrate awareness of edge cases and production considerations - this is what separates good answers from great ones.

Expert Answer
103 words

Architectural Logic: SCD types trade history depth vs storage and complexity. Type 1: Overwrite; no history. Use when history irrelevant (typo correction). Type 2: Full history; new row on change; effective_from, effective_to, current_flag. Use when history needed (customer address, department). Type 3: Limited history; previous value in column. Use when only last change matters. Implementation: Type 1 = UPDATE; Type 2 = INSERT new + UPDATE current; Type 3 = UPDATE shift. Scalability: Type 2 grows rows; Type 1 and 3 are stable. Cost: Type 2 increases storage and join complexity. Best Practice: Choose by business need; Type 2 most common for dimensions.

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