Database developers design, implement, and maintain databases to store and organize data efficiently. They need strong knowledge of database management systems, SQL, optimization, and data modeling. Below are 25 common Database Developer interview questions with answers to help you prepare thoroughly.
Q1. What is a database?
A database is an organized collection of data that can be easily accessed, managed, and updated.
Q2. What is SQL?
SQL (Structured Query Language) is a standard programming language used to manage and manipulate relational databases.
Q3. What are the different types of databases?
Relational databases (e.g., MySQL, PostgreSQL), NoSQL databases (e.g., MongoDB, Cassandra), in-memory databases, and graph databases.
Q4. What is normalization?
Normalization is the process of organizing data to minimize redundancy and improve data integrity by dividing data into related tables.
Q5. What are the normal forms?
First Normal Form (1NF), Second Normal Form (2NF), Third Normal Form (3NF), Boyce-Codd Normal Form (BCNF), and others, each with specific rules to reduce redundancy.
Q6. What is a primary key?
A primary key is a unique identifier for each record in a database table.
Q7. What is a foreign key?
A foreign key is a field in one table that uniquely identifies a row of another table, establishing a relationship between tables.
Q8. What is indexing?
Indexing improves database query performance by creating data structures that allow faster retrieval of records.
Q9. What is a stored procedure?
A stored procedure is a precompiled set of SQL statements stored in the database that can be executed repeatedly.
Q10. What are triggers?
Triggers are special procedures that automatically execute in response to certain events on a table, such as INSERT, UPDATE, or DELETE.
Q11. What is ACID in databases?
ACID stands for Atomicity, Consistency, Isolation, Durability — key properties ensuring reliable transactions.
Q12. What is a transaction?
A transaction is a unit of work that is performed completely or not at all, ensuring data integrity.
Q13. What is the difference between DELETE and TRUNCATE?
DELETE removes rows one by one and can be rolled back; TRUNCATE removes all rows quickly and cannot be rolled back in most databases.
Q14. What is denormalization?
Denormalization is the process of adding redundant data to improve read performance at the expense of write speed and data integrity.
Q15. What is a view?
A view is a virtual table representing the result of a stored query.
Q16. How do you optimize SQL queries?
Use indexes, avoid SELECT *, minimize joins, use appropriate WHERE clauses, and analyze query execution plans.
Q17. What are joins? Name the types.
Joins combine rows from two or more tables based on a related column. Types: INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL OUTER JOIN.
Q18. What is a clustered index?
A clustered index determines the physical order of data in a table and improves retrieval speed.
Q19. What is a non-clustered index?
A non-clustered index is a separate data structure that points to the physical data location, allowing quick lookups.
Q20. What is a schema?
A schema is the structure or blueprint of a database that defines tables, relationships, views, and other objects.
Q21. What are the differences between OLTP and OLAP?
OLTP (Online Transaction Processing) focuses on transaction-oriented tasks; OLAP (Online Analytical Processing) is used for complex queries and analysis.
Q22. What is data integrity?
Data integrity ensures accuracy, consistency, and reliability of data throughout its lifecycle.
Q23. What are constraints?
Constraints enforce rules on data columns, such as NOT NULL, UNIQUE, CHECK, PRIMARY KEY, and FOREIGN KEY.
Q24. What is a deadlock?
A deadlock occurs when two or more transactions wait indefinitely for each other to release locks.
Q25. How do you handle database backup and recovery?
By scheduling regular backups, using transaction logs, and having recovery plans to restore data after failures.