Reviewed by Aditya Kumar · Last reviewed 2026-08-08
Handling schema mismatches during merging involves strategies like schema evolution for additive changes, explicit mapping for complex transformations, and robust validation to ensure data integrity,…
Pro-Move: 'Two sources added column at different times. We use unionByName; new columns default null. Backfill job filled historical.'
This easy-level System Design/Architecture question appears frequently in data engineering interviews at companies like Virtusa. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (spark) will help you answer variations of this question confidently.
Start by clearly defining the core concept being asked about. Interviewers want to see that you understand the fundamentals before diving into implementation details. Structure your answer with a definition, then explain the practical application with a concise example.
Handling schema mismatches during merging involves strategies like schema evolution for additive changes, explicit mapping for complex transformations, and robust validation to ensure data integrity, gracefully combining datasets with differing structures.
NULL or defaults) or making existing columns nullable. Data lake formats like Delta Lake support this, tracking schema changes and minimizing disruption.old_name AS new_name), casting data types (CAST(col AS INT)), or providing NULLs/defaults for missing columns. ThisPro-Move: 'Two sources added column at different times. We use unionByName; new columns default null. Backfill job filled historical.'
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According to DataEngPrep.tech, this is one of the most frequently asked System Design/Architecture interview questions, reported at 1 company. DataEngPrep.tech maintains an editor-reviewed database of 1,863 data engineering interview questions across 7 categories.