Choosing Your Strategy

Concepts covered: dmScdStrategy

Per-Attribute Strategy The most important concept: SCD type is chosen per attribute, not per table. A single dim_customer can have Type 1 on name (typo corrections do not need history), Type 2 on region (revenue attribution needs point-in-time accuracy), and Type 3 on segment (before/after comparison for a migration). The decision for each attribute: does anyone need the historical value? If the answer is 'yes, for reporting or audit,' use Type 2. If the answer is 'no, and keeping it creates useless rows,' use Type 1. If the answer is 'only the immediately previous value, for a specific comparison,' Type 3.

About This Interactive Section

This section is part of the Change Tracking lesson on DataDriven, a free data engineering interview prep platform. Each section includes explanations, worked examples, and hands-on code challenges that execute in real time. SQL queries run against a live PostgreSQL database. Python runs in a sandboxed Docker container. Data modeling problems validate against interactive schema canvases. All content is framed around what data engineering interviewers actually test at companies like Meta, Google, Amazon, Netflix, Stripe, and Databricks.

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DataDriven combines four interview rounds (SQL, Python, Data Modeling, Pipeline Architecture) with adaptive difficulty and spaced repetition. Easy problems get harder as you improve. Weak concepts resurface until you master them. Your readiness score tracks progress across every topic interviewers test. Every lesson section ends with problems you solve by writing and running real code, not by picking multiple-choice answers.