Reviewed by Aditya Kumar · Last reviewed 2026-03-24
**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...
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.
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.
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.
Red Flag: Using Type 1 for attributes that need audit trail—compliance risk. Pro-Move: State business requirement first; Type 2 for regulatory; mention effective dates and current_flag; reference late-arrival handling.
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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 an editor-reviewed database of 1,863 data engineering interview questions across 7 categories.