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Normalization & Slowly Changing Dimensions (SCD) Type 2

SQLeasy0.4 min readPremium
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
Walmart
Key Concepts Tested
etl
Expert AnswerPremium
82 wordsInterview-ready
SCD Type 2: history by adding rows. New row for each change with effective/expiry dates. Columns: surrogate_key, natural_key, attributes, effective_date, end_date, is_current. On change: set end_date on current row, insert new row with effective_date=now, end_date=infinity. Query current: WHERE is_current=1. Use for: dimension history (customer, product). Requires careful ETL to maintain timeline. **Why it matters**: Design choices compound at scale—wrong approach can cause 100× overhead....
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