DBMS Interview Questions and Answers

CTA

Most Frequently Asked Dbms Interview Questions

1. What is DBMS?
2. What is RDBMS?
3. What are the differences between DBMS and RDBMS?
4. What is a database?
5. List out the database languages.
6. What are the different types of database systems?
7. What are the different types of database queries?
8. What is the ER diagram in DBMS?
9. Define a relation schema.
10. What is normalization in DBMS?

Database Management Systems (DBMS) are essential for storing and managing large amounts of data. If you are interviewing for a job that involves DBMS, it is important to be prepared for the DBMS interview questions that you may be asked.

This blog post will give you an overview of the most frequently asked DBMS interview questions. By understanding these questions, you can increase your chances of success in your next interview.

Basic DBMS Interview Questions

1. What is DBMS?

DBMS stands for Database Management System. It is used to store, retrieve, manage, and organize the data in the database. It defines the structure of the database and acts as an intermediary between the users and the data.

2. What is RDBMS?

RDBMS stands for Relational Database Management System. In RDBMS, the data is structured in table format. Each table represents an entity, a relationship between entities, or a relationship between entities in the real-world domain.

3. What are the differences between DBMS and RDBMS?

4. What is a database?

A database is a collection of structured data stored in a system. It is used to store, retrieve, and manage huge amounts of data. The data is organized in table format. Each table will have rows and columns to represent the structure of the data.

5. List out the database languages.

The types of database languages are listed below.

6. What are the different types of database systems?

There are two main types of database systems: relational and non-relational databases.

• Relational databases are the most common type of database system. They use a relational model to store data, which means that the data is stored in tables that are related to each other by common keys. 
• Non-relational databases are a newer type of database system that can store data in a variety of formats, including graphs, documents, and JSON objects.

7. What are the different types of database queries?

There are three main types of database queries:

• SELECT queries are used to retrieve data from a database.
• INSERT queries are used to add data to a database.
• UPDATE queries are used to modify data in a database.

8. What is the ER diagram in DBMS?

An Entity-Relationship (ER) diagram is a visual representation of the entities (objects or concepts) and the relationships between them in a database management system (DBMS). It is a modeling technique used to design and represent the structure of a database.

9. Define a relation schema.

Relation schemas are often depicted using entity-relationship diagrams (ER diagrams) that visually represent the relationships between entities. They help database designers and developers understand and define the structure of the database, allowing for effective data organization, retrieval, and manipulation.

10. What is normalization in DBMS?

Normalization is the process of designing a database so that the data is stored in a way that is efficient and easy to maintain.

11. What is denormalization?

Denormalization is the process of adding redundancy to a database in order to improve performance.

12. What is a primary key?

A primary key is a unique identifier for a row in a table. A primary key can be a single column or a combination of columns.

13. What is a foreign key?

A foreign key is a column in a table that references a primary key in another table. Foreign keys are used to establish relationships between tables.

14. What is a database constraint?

A database constraint is a rule that is enforced on a database table. Constraints can be used to enforce data integrity, such as ensuring that a column can only contain a certain type of data or that a column cannot be left blank.

15. What is a database view?

A database view is a virtual table that is created from one or more tables. Views can be used to simplify complex queries, hide sensitive data, or provide a different perspective on the data.

16. Discuss the differences between a primary key and a unique key in a database.

17. What is the purpose of the EXISTS keyword in SQL queries?

The EXISTS keyword is used to check if any rows in a table satisfy a given condition.

18. What is the purpose of the GRANT and REVOKE statements in DBMS?

The GRANT statement is used to give users permission to access a database or table. The REVOKE statement is used to take away permission from users.

19. What is the difference between a view and a table in a DBMS?

A view is a virtual table that is created from one or more tables. It does not contain any data of its own but rather provides a way to see the data from one or more tables in a different way. A table is a physical object that contains data.

20. What is the purpose of the COMMIT and ROLLBACK statements in DBMS?

The COMMIT statement is used to make permanent all changes that have been made to a database since the last COMMIT or ROLLBACK statement. The ROLLBACK statement is used to undo all changes that have been made to a database since the last COMMIT or ROLLBACK statement.

Intermediate DBMS Interview Questions

21. Explain ACID properties.

ACID stands for Atomicity, Consistency, Isolation, and Durability.

• Atomicity: Atomicity guarantees that a transaction is handled as an indivisible and coherent unit of work. This implies that all the operations within the transaction must either succeed entirely or fail completely. If any portion of the transaction encounters an error, all modifications made by the transaction are undone, leaving the database unaffected. Ultimately, atomicity ensures that the database maintains a consistent state before and after the execution of a transaction.
• Consistency: Consistency ensures that a transaction moves the database from one valid state to another by defining a specific set of rules or constraints that the data must follow. These rules can include integrity constraints, data validation rules, and other business rules. Consistency ensures that a transaction preserves data integrity and does not violate any defined rules or constraints.
• Isolation: Isolation guarantees that concurrent transactions operate independently and do not interfere with each other. It means that each transaction must be executed in isolation without being affected by other transactions running concurrently. Isolation is crucial to maintain data integrity and prevent issues like non-repeatable reads, dirty reads, and phantom reads. Database systems use various isolation levels, such as Read Uncommitted, Read Committed, Repeatable Read, and Serializable, to control the level of isolation between transactions.
• Durability: Durability provides assurance that after a transaction is committed, its modifications are permanently saved and will endure any potential system failures, like power outages or crashes. The changes made by a committed transaction are securely stored in non-volatile memory, usually on disk storage, ensuring their long-lasting durability. Even in the event of a system failure, the database can recover the committed transactions and restore the data to its last consistent state.

22. What is a database trigger?

A database trigger is a piece of code that is executed when an event occurs in a database. Events that can cause a database trigger include insert, update, and delete operations.

23. What is a database stored procedure?

A database stored procedure is a collection of SQL statements that are stored in the database. Stored procedures can be used to perform complex tasks such as inserting, updating, and deleting data or running reports.

24. What is a database backup?

A database backup is a copy of a database that is created for the purpose of disaster recovery. Database backups can be created manually or automatically.

25. What is database recovery?

A database recovery is the process of restoring a database from a backup. Database recovery can be necessary in the event of a disaster, such as a hardware failure or software corruption.

26. What is the purpose of the UNIQUE constraint in a DBMS?

A UNIQUE constraint is a database constraint that ensures that no two rows in a table have the same value for a particular column. This helps ensure the uniqueness of data in a database.

27. What is a surrogate key? When and why is it used in a DBMS?

A surrogate key is a unique identifier that is not related to the meaning of the data in a database. It is often used when a natural key (such as a customer name or product ID) is not unique. Surrogate keys are used to improve performance and data integrity.

28. What is the concept of data warehousing in a DBMS?

Data warehousing is the process of collecting data from a variety of sources and storing it in a central location for analysis. This data can be used to make decisions about business operations, such as which products to sell, where to open new stores, and how to market products.

29. What is the difference between a schema and a database in DBMS?

A schema is a blueprint for a database. It defines the tables, columns, and relationships in a database. A database is a collection of data that is organized according to a schema.

30. What is the difference between a distributed database and a centralized database?

A distributed database is a database that is spread across multiple computers. A centralized database is a database that is stored on a single computer.

31. What is the difference between a single-user and a multi-user DBMS?

A single-user DBMS can only be used by one user at a time. A multi-user DBMS can be used by multiple users at the same time.

32. What are the different types of database transactions?

Read committed transactions allow other users to read data that has been committed by a transaction, but they do not allow other users to see data that has been modified but not yet committed.

Repeatable read transactions prevent other users from modifying data that has been read by a transaction.

33. What is the concept of data integrity constraints in a DBMS?

Data integrity constraints are rules that ensure the accuracy and consistency of data in a database. They can be used to prevent data from being entered incorrectly, to ensure that data is updated consistently, and to prevent data from being accidentally deleted.

Advanced DBMS Interview Questions

34. Explain the architecture of SQL.

This is the Architecture of SQL:

35. What are the benefits of using a database system?

• Data Integrity: Database systems can help ensure that data is stored accurately and consistently.
• Data Security: Database systems can help protect data from unauthorized access.
• Data Performance: Database systems can help improve the performance of queries and data access.
• Data Scalability: Database systems can be scaled to handle large amounts of data.

36. What are the different types of database locks?

There are two main types of database locks: shared locks and exclusive locks.

• Shared locks prevent other transactions from modifying data that is being read by a transaction.
• Exclusive locks prevent other transactions from reading or modifying data that is being modified by a transaction.

37. What are the different types of database replication?

There are two main types of database replication: master-slave and master-master replications.

• Master-slave replication creates a master database and one or more slave databases. The master database is the only database that can be updated. The slave databases are updated with the changes from the master database.
• Master-master replication creates two or more databases that can all be updated. The changes made to one database are automatically applied to all of the other databases.

38. What are the different types of database isolation levels?

There are four main types of database isolation levels:

• Read Committed: is the default isolation level. It allows other users to read data that has been committed by a transaction, but it does not allow other users to see data that has been modified but not yet committed.
• Repeatable: Repeatable reading prevents other users from modifying data that has been read by a transaction.
• Serializable: Serializable ensures that all transactions see the same data, even if other transactions modify it.
• Read Uncommitted: It stands as the most lenient among all isolation levels. Under this level, a transaction can access data modifications made by other transactions even before they are committed, resulting in the possibility of reading uncommitted or “dirty” data. Transactions at this level are not isolated from each other, meaning concurrent transactions may interfere with each other’s data, potentially leading to data inconsistencies or errors.

39. What are the different types of database administration?

There are two main types of database administration: operational and strategic. 

• Operational database administration is responsible for the day-to-day tasks of managing a database, such as creating and maintaining user accounts, monitoring performance, and resolving problems. 
• Strategic database administration is responsible for the long-term planning and development of a database, such as designing the database schema, developing security policies, and implementing disaster recovery procedures.

40. What are the different types of database developers?

There are two main types of database developers: application developers and database architects. 

• Application developers are responsible for developing applications that use databases. 
• Database architects are responsible for designing and implementing databases.

41. What are the different types of database tools?

Different types of database tools are available, including database development tools, database administration tools, and database reporting tools. Database development tools are used to create and modify database schemas. Database administration tools are used to manage databases, such as by creating and maintaining user accounts, monitoring performance, and resolving problems. Database reporting tools are used to generate reports from data stored in a database.

42. What are the future trends in database technology?

The future trends in database technology include the increasing use of cloud computing, the growth of big data, and the development of new database technologies such as NoSQL and NewSQL.

43. What are the advantages of using an object-oriented database management system?

OODBMSs offer a number of advantages over traditional relational database management systems (RDBMSs). They allow data to be stored in objects, which are more natural for representing real-world entities. They also allow relationships between objects to be defined more easily.

44. Discuss the differences between a clustered and a non-clustered index.

Clustered and non-clustered indexes are fundamental concepts in database management systems. A clustered index determines the physical order of data within a table, where rows are sorted based on the indexed column. As a result, a table can have only one clustered index. On the other hand, a non-clustered index creates a separate structure, containing a copy of the indexed column’s values and a reference to the corresponding rows. Consequently, multiple non-clustered indexes can exist for a table. While clustered indexes are beneficial for frequently searched columns, non-clustered indexes are preferable for improving the speed of SELECT queries on various columns without altering the physical data order.

45. Explain the concept of database caching and its benefits.

Database caching is the process of storing frequently accessed data in a temporary cache memory to expedite data retrieval and enhance system performance. When a user or application requests data, the system first checks the cache. If the data is present, it is swiftly returned, reducing the need for resource-intensive database queries. This results in significant performance gains, reduced latency, and improved response times. Caching also alleviates database server loads, ensuring efficient resource utilization. Moreover, it enhances scalability, enabling the system to handle more concurrent users and data requests effectively. Overall, implementing database caching optimizes system efficiency and delivers a seamless user experience.

46. Explain the concept of database denormalization and its use cases.

Database denormalization is the deliberate process of introducing redundancy into a relational database by consolidating data from multiple tables into one. This departure from the principles of normalization aims to enhance performance and simplify data retrieval. Denormalization reduces the need for complex joins, thereby improving query execution speed, especially in read-heavy applications. It is particularly beneficial in data warehousing, analytical, and reporting systems where quick access to large datasets is crucial. However, denormalization requires careful consideration as it can lead to data integrity issues and increased storage requirements. Its strategic application should be based on specific performance requirements and trade-offs.

47. What is the concept of database synchronization in a DBMS?

Database synchronization is the process of keeping multiple copies of a database consistent. This is important in distributed databases, where multiple users may be accessing the same data at the same time.

48. Explain the concept of data partitioning in a DBMS and its advantages.

Data partitioning in a DBMS refers to the practice of dividing large datasets into smaller, manageable segments, which are distributed across different physical storage locations. This technique offers several advantages. Firstly, it enhances performance by reducing the amount of data accessed during queries, thus minimizing response times. Secondly, data partitioning enables parallel processing, leading to improved system scalability and throughput. Thirdly, it optimizes data storage and retrieval operations, as each partition can be independently managed and maintained. Overall, data partitioning in a DBMS ensures efficient data management, better performance, and supports the handling of large datasets, making it a valuable strategy in modern database architectures.

49. Explain the concept of a foreign key cascade update in a DBMS.

In a Database Management System (DBMS), a foreign key cascade update is a referential integrity constraint that automatically updates related records in child tables when changes are made to the primary key in the parent table. 

For instance, if a primary key value is modified in a parent table, all corresponding foreign key values in associated child tables are automatically updated to maintain data consistency. An example is a ‘Customers’ table (parent) linked to an ‘Orders’ table (child), where changing a customer’s ID in the parent table updates all corresponding order records in the child table.

50. What is the purpose of a data dictionary in a DBMS?

A data dictionary in a Database Management System (DBMS) serves the vital purpose of providing a comprehensive repository of metadata, and defining data structures, attributes, relationships, and constraints within a database. It enhances data integrity, facilitates efficient data management, and aids in database schema design. For instance, in a healthcare DBMS, a data dictionary would detail patient records, specifying fields like ‘patient ID’, ‘name’, ‘DOB’, and associated constraints, streamlining data organization and retrieval.