Top 10 Database Questions in 2026
Top 10 Database Questions in 2026 uses verified RivoHire qbank answers. Start with the strongest short answer, then review tradeoffs, scenarios, mistakes, and interview wording.
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By the end of this guide, you will:
- A SQL change causes slower responses after traffic increases. I would isolate the hot path, apply the smallest reversible fix, and verify the result with latency, error rate, and rollback readiness.
- A SQL change causes slower responses after traffic increases. I would isolate the hot path, apply the smallest reversible fix, and verify the result with latency, error rate, and rollback readiness.
- A SQL change causes slower responses after traffic increases. I would isolate the hot path, apply the smallest reversible fix, and verify the result with latency, error rate, and rollback readiness.
- A SQL change causes slower responses after traffic increases. I would isolate the hot path, apply the smallest reversible fix, and verify the result with latency, error rate, and rollback readiness.
Coding question collection
Interview Questions With Code Practice
Each question includes the prompt, interview explanation, language tabs, a code-editor style solution, and time and space complexity notes.
Difficulty Distribution
1. What is the difference between WHERE and HAVING?
WHERE filters rows before grouping, while HAVING filters groups after aggregation.
WHERE filters rows before grouping, while HAVING filters groups after aggregation. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
2. What is the difference between INNER JOIN and LEFT JOIN?
INNER JOIN returns matching rows from both tables, while LEFT JOIN keeps all left-table rows and fills missing matches with nulls.
INNER JOIN returns matching rows from both tables, while LEFT JOIN keeps all left-table rows and fills missing matches with nulls. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
3. How do indexes affect SQL write performance?
Indexes speed reads but slow writes because each insert, update, or delete may also update index structures.
Indexes speed reads but slow writes because each insert, update, or delete may also update index structures. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
4. What is a deadlock in SQL databases?
A deadlock occurs when transactions wait on each other's locks and none can proceed.
A deadlock occurs when transactions wait on each other's locks and none can proceed. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
5. What is a window function?
A window function calculates values across a set of related rows without collapsing the result into one row per group.
A window function calculates values across a set of related rows without collapsing the result into one row per group. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
6. What are ACID properties?
ACID means atomicity, consistency, isolation, and durability for reliable transaction processing.
ACID means atomicity, consistency, isolation, and durability for reliable transaction processing. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
7. How would you debug a production issue in SQL?
Start with symptoms, compare recent changes, inspect logs and metrics, isolate the failing path, and apply the smallest safe fix.
Start with symptoms, compare recent changes, inspect logs and metrics, isolate the failing path, and apply the smallest safe fix. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
8. What tradeoffs matter most in SQL?
The key tradeoffs are correctness, performance, complexity, cost, maintainability, and how easily the team can operate the solution.
The key tradeoffs are correctness, performance, complexity, cost, maintainability, and how easily the team can operate the solution. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
9. How would you explain SQL to a junior teammate?
Use a small example, explain the problem it solves, show the happy path, then discuss the first edge case they should watch for.
Use a small example, explain the problem it solves, show the happy path, then discuss the first edge case they should watch for. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
10. What common mistake should developers avoid in SQL?
Avoid applying a pattern before measuring the problem or understanding the constraints that make the pattern useful.
Avoid applying a pattern before measuring the problem or understanding the constraints that make the pattern useful. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
FAQ
What is the difference between WHERE and HAVING?
WHERE filters rows before grouping, while HAVING filters groups after aggregation. In an interview, support it with one tradeoff and one production example.
What is the difference between INNER JOIN and LEFT JOIN?
INNER JOIN returns matching rows from both tables, while LEFT JOIN keeps all left-table rows and fills missing matches with nulls. In an interview, support it with one tradeoff and one production example.
How do indexes affect SQL write performance?
Indexes speed reads but slow writes because each insert, update, or delete may also update index structures. In an interview, support it with one tradeoff and one production example.
What is a deadlock in SQL databases?
A deadlock occurs when transactions wait on each other's locks and none can proceed. In an interview, support it with one tradeoff and one production example.
What is a window function?
A window function calculates values across a set of related rows without collapsing the result into one row per group. In an interview, support it with one tradeoff and one production example.
What are ACID properties?
ACID means atomicity, consistency, isolation, and durability for reliable transaction processing. In an interview, support it with one tradeoff and one production example.
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