SQL NULL Handling Interview Questions

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

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

Related SQL concepts

• SQL JOIN interview questions
• SQL aggregation interview questions
• SQL CASE WHEN interview questions
• SQL CTE and subquery interview questions