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Data ScientistIdentify Top Users with Declined Transactions in SQL
Data Manipulation (SQL/Python)
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August 4, 2025
SQL NULL Handling Interview Questions
NULL handling questions test whether you understand three-valued logic and how NULLs affect filters, joins, and aggregates.
Expect COALESCE, NULLIF, IS NULL, and NULL-safe comparisons in realistic scenarios.
Interviewers care about correctness and edge cases with missing data.
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18Companies
Common SQL NULL handling interview patterns
- Replacing NULLs with defaults using COALESCE
- Filtering missing data with IS NULL / IS NOT NULL
- NULL behavior in LEFT JOINs
- NULL-safe comparisons in conditional logic
- Handling NULLs in aggregates
SQL NULL handling interview questions
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Medium
Data EngineerCompute cumulative metrics with full joins
Data Manipulation (SQL/Python)
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August 1, 2025
Common mistakes with SQL NULL handling
- Using = NULL instead of IS NULL
- Filtering NULLs in WHERE after a LEFT JOIN
- COUNT(column) vs COUNT(*) misunderstandings
- Forgetting NULLs in CASE conditions
- Assuming NULL equals empty string or zero
How NULL handling questions are evaluated in interviews
Correct treatment of missing data is the main signal.
Explain how NULLs flow through joins, filters, and aggregates.
State assumptions when the data model is ambiguous.