Commonly Asked Database Interview Questions

By Pooja Ghodekar
June 28, 2024
SQL

Commonly Asked Database Interview Questions

Discover the most commonly asked database interview questions to prepare effectively. Enhance your knowledge on SQL, DBMS, keys, indexing, and more.

1. What is a Database?

Explain what a database is and the purpose it serves.

2. What is a DBMS (Database Management System)?

Describe what a DBMS is and provide examples.

3. What is SQL?

What are the different types of SQL commands?

4. What is a primary key?

Define a primary key and its importance.

5. What is a foreign key?

Explain the concept of a foreign key and its role in a database.

6. What is a unique key?

Describe what a unique key is and how it differs from a primary key.

SQL Queries

7. How do you write a basic SQL query to select all records from a table?

Example: SELECT * FROM table_name;

8. How do you delete records from a table?

Example: DELETE FROM table_name WHERE condition;

9. How do you use the WHERE clause in a query?

Provide an example of using the WHERE clause to filter data.

Data Types and Constraints

10. What are data types in SQL?

11. What are the constraints in SQL?

Describe constraints like NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, CHECK, and DEFAULT.
What is a CHECK constraint?

Advanced SQL Queries

12. What is a CASE statement in SQL?

Provide an example of a CASE statement and explain its use.

13. How do you perform a UNION operation in SQL?

Explain how UNION combines the result sets of two or more SELECT statements.

Database Design

14. What is an ERD (Entity-Relationship Diagram)?

Explain what an ERD is and its purpose in database design.

15. What are the different types of relationships in a database?

Discuss one-to-one, one-to-many, and many-to-many relationships.

16. What is database schema?

Define database schema and its components.

Transactions and Locking

17. What is a savepoint in SQL?

Explain what a savepoint is and how it is used in transactions.

18. What are locks in databases?

Describe different types of locks (e.g., shared, exclusive) and their purposes.
Explain what a deadlock is and strategies to prevent or resolve it.

Indexing and Performance

19. What are the different types of indexes?

Discuss clustered and non-clustered indexes.
How do you create an index in SQL?
- Example: CREATE INDEX index_name ON table_name (column_name);
What is the impact of indexing on performance?
- Explain both the positive and negative impacts of indexing on database performance.

Functions and Aggregations

20. What are Aggregate Functions in SQL?

Explain and provide examples of aggregate functions like SUM, AVG, MIN, MAX, and COUNT.

21. How do you use the GROUP BY clause?

Provide an example of the GROUP BY clause to aggregate data.

22. What is the HAVING clause used for?

Explain the use of the HAVING clause with an example.

Stored Procedures and Triggers

23. What is a trigger in SQL?

Describe what a trigger is and give an example of its use.

24. How do you create a stored procedure?

Example: CREATE PROCEDURE procedure_name AS BEGIN — SQL statements END;
What are the advantages of using stored procedures?
- Discuss the benefits, such as performance improvements, reusability, and security.

Note: Prepare for your interview with these essential SQL interview questions and answers. Master key concepts and enhance your SQL knowledge to ace the interview.

Miscellaneous

25. What is a cursor in SQL?

Explain what a cursor is and provide an example of its use.

26. What is the difference between ROWNUM and ROW_NUMBER() in SQL?

Describe the differences between these two functions.

27. What are views, and how do they differ from tables?

Explain what views are and their advantages over tables.

Scenario-Based Questions

28. How do you handle duplicate rows in a result set?

Discuss methods such as using DISTINCT or handling duplicates in the application layer.

29. Write a query to find employees with salaries above the department average.

Example: SELECT * FROM employees WHERE salary > (SELECT AVG(salary) FROM employees GROUP BY department_id);

30. What steps would you take to secure a database?

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General Understanding

31. Explain the term data integrity.

Describe what data integrity means and its importance in databases.

32. What is an OLTP system?

Define OLAP (Online Analytical Processing) and its use cases.

33. How would you handle exceptions in SQL?

Discuss methods to handle exceptions in SQL, such as using TRY…CATCH.

34. How do you optimize a SQL query?

Provide tips on query optimization, like indexing and query refactoring.

General Questions

35. What are some common database design best practices?

Discuss best practices such as normalization, indexing, and consistent naming conventions.

36. Describe the responsibilities of a DBA.

Conceptual Understanding

37. What is a view in SQL?

Describe what a view is and its benefits.

38. What is a subquery?

39. What is the difference between HAVING and WHERE?

Clarify the difference between the HAVING clause and the WHERE clause.

40. What is the difference between CHAR and VARCHAR?

Explain the differences and when to use each data type.

41. What is a cursor in SQL?

Explain what a cursor is and provide an example of its use.

42. What is the difference between ROWNUM and ROW_NUMBER() in SQL?

Describe the differences between these two functions.

43. What are views, and how do they differ from tables?

Explain what views are and their advantages over tables.

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Author:-

Pooja Ghodekar

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