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What is the purpose of Delta format, and how does it differ from Parquet in terms of storage and querying?

SQLeasy0.5 min read

Delta format: Built on Parquet with transaction log (ACID), time travel, and upserts. Supports MERGE, DELETE, UPDATE. Parquet: Immutable columnar format; append-only; no built-in ACID. Delta adds: schema enforcement, compaction, change data feed. Storage: Both columnar; Delta...

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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
Tredence

Why This Question Matters

This easy-level SQL question appears frequently in data engineering interviews at companies like Tredence. While less common, it tests deeper understanding that distinguishes strong candidates.

How to Approach This

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.

Expert Answer
90 words

Delta format: Built on Parquet with transaction log (ACID), time travel, and upserts. Supports MERGE, DELETE, UPDATE. Parquet: Immutable columnar format; append-only; no built-in ACID. Delta adds: schema enforcement, compaction, change data feed. Storage: Both columnar; Delta adds _delta_log. Querying: Delta supports point-in-time reads; Parquet is file-atom. Use Delta for mutable tables, pipelines needing upserts; Parquet for immutable batches. 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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