Teradata to Hadoop migration with SCD Type 2 requires careful planning. Key steps: (1) Schema mapping—map Teradata tables to Hive/Spark equivalents; handle Teradata-specific functions. (2) SCD Type 2 logic—maintain current and historical rows using effective_date,...
This medium-level SQL question appears frequently in data engineering interviews at companies like Citi. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (join, partition, spark) 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.
Teradata to Hadoop migration with SCD Type 2 requires careful planning. Key steps: (1) Schema mapping—map Teradata tables to Hive/Spark equivalents; handle Teradata-specific functions. (2) SCD Type 2 logic—maintain current and historical rows using effective_date, effective_end_date, and is_current flag. In Spark: use MERGE (Delta) or upsert logic with window functions to detect changes. (3) Migration strategy—batch historical load first, then CDC for ongoing changes. Use staging tables to validate row counts and checksums before cutover. (4) Performance—partition SCD tables by effective_date; use bucketing for join keys. Example: For customer dimension, compare source hash with target; insert new versions and update is_current on previous row. Validate with reconciliation queries post-migration. Why it matters: Design choices compound at scale—wrong approach can cause 100× overhead. Scalability trade-offs: Profile before optimizing; validate on sample then full. Cost implications: Suboptimal choices multiply at billion-row scale.
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Analyze My Answer — FreeAccording to DataEngPrep.tech, this is one of the most frequently asked SQL interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.