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Home/Questions/SQL/What are Slowly Changing Dimensions (SCD), and how would you implement them for tracking customer data changes?

What are Slowly Changing Dimensions (SCD), and how would you implement them for tracking customer data changes?

SQLmedium0.7 min readPremium
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Asked at 1 company
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487
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130E|271M|86H
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1,863
across 7 categories
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Swiggy
Key Concepts Tested
partitionsparksqlwindow
Expert AnswerPremium
144 wordsInterview-ready
Slowly Changing Dimensions (SCD) track historical changes in dimension data. Types: Type 1 (overwrite), Type 2 (full history), Type 3 (previous + current). For customer tracking, SCD Type 2 is common: add effective_date, end_date, is_current. On change: set end_date=now() and is_current=false on current row; insert new row with is_current=true. Implementation: Use MERGE in SQL or Delta Lake, or Spark with window functions to detect changes....
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