Introduction

SQL remains the cornerstone of database management. Whether you’re hiring for an analyst position, a backend developer role, or any job requiring database interactions, evaluating SQL knowledge is paramount. Here are ten insightful SQL interview questions to gauge the depth of a candidate's understanding:

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Questions

1. Explain the Difference Between INNER JOIN and LEFT JOIN.

Purpose: Understanding of basic joins and their applications.

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2. What is an SQL View? How is it Different from a Table?

Purpose: Assessing comprehension of virtual tables and database structuring.

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3. Describe Normalization and Denormalization. Why are They Important?

Purpose: Evaluating knowledge on database optimization techniques.

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4. How Do You Retrieve the Nth Highest Salary from a Table Without Using LIMIT or OFFSET?

Purpose: Tests depth of SQL knowledge and problem-solving ability.

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5. Describe a SQL Injection. How Can It Be Prevented?

Purpose: Understanding of SQL vulnerabilities and security best practices.

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6. Explain the Functionality of the DISTINCT and GROUP BY clauses. How Do They Differ?

Purpose: Grasping aggregate functions and data retrieval methods.

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7. How Do Transactions Work in SQL? Why are They Useful?

Purpose: Assessing understanding of the database transaction and its significance in ensuring data integrity.

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8. Can You Write a SQL Query to Find Duplicate Records Without Using the DISTINCT Keyword?

Purpose: Testing proficiency in crafting complex queries.

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9. Explain Indexing in SQL. Why is It Important?

Purpose: Understanding of performance optimization techniques and how indexing speeds up data retrieval processes.

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10. What's the Difference Between DELETE and TRUNCATE Commands?

Purpose: Comprehending different data removal methods and their implications.

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In Conclusion

Interviewing for SQL expertise requires a blend of theoretical and practical questions. These ten queries aim to test a candidate's foundational knowledge, their problem-solving ability, and their grasp of best practices. Dive deep into their responses, and you'll get a clear picture of their SQL proficiency.

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