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How do quarantine tables ensure data quality in downstream pipelines?

SQLeasy0.3 min readPremium

**Quarantine tables** store rows failing validation (schema, business rules, duplicates). Downstream reads only from validated path—ensuring quality. **Flow**: Validate → route pass to main, fail to quarantine. **Schema**: Mirror main + error_code, error_message, reject_reason....

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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
PWC

Why This Question Matters

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

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Expert Answer
59 words

Quarantine tables store rows failing validation (schema, business rules, duplicates). Downstream reads only from validated path—ensuring quality. Flow: Validate → route pass to main, fail to quarantine. Schema: Mirror main + error_code, error_message, reject_reason. Governance: Periodic review; remediate or discard; alert on volume spike. Why: Prevents bad data propagation; traceability for debugging. Cost: Storage for quarantine; ops for review.

The complete answer continues with detailed implementation patterns, architectural trade-offs, and production-grade considerations covering performance optimization and real-world examples.

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According 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.

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