DBMS Top 50 Most Important Interview Questions

DBMS Interview Questions and Answers

In today's digital world, data is everything, so Database Management Systems have become crucial to efficiently managing huge amounts of information. These software systems are used not just for storing data but also for retrieving and running queries on it.

In this DBMS Tutorial, we will try to explore some of the most important DBMS interview questions and answers that will help you ace your next interview. They have been categorized for you as DBMS interview questions for freshers, and DBMS interview questions for experienced. You can learn all of these topics from basics as well through this SQL Server Certification Training.

DBMS Interview Questions & Answers for Beginners

1. What is a DBMS?

A DBMS is also known as a Database Management System.  It is software that helps its users work with databases easily. It lets them create, read, update, and manage databases. It provides a user interface through which data can be handled without having to write codes.

2. What are the advantages of using a DBMS?

Some benefits of using a DBMS are as follows:

• It ensures that the data is accurate and consistent.
• To protect it against unauthorized users, it helps in managing access to data.
• It allows for changes to be made in the application without affecting the system components by separating them from each other.
• It helps in providing efficient mechanisms for storing retrieving and manipulating data.
• It also supports backup and recovery processes to prevent data loss.

3. What are the different types of DBMS?

The primary types of DBMS include:

1. Relational DBMS (RDBMS), which organizes data into tables using SQL for querying.
2. NoSQL DBMS, tailored for structured data with flexible schemas.
3. Object-oriented DBMS stores data as objects following the object-oriented programming principles.
4. Hierarchical DBMSarranges data in a tree structure where parent records are related to child records through pointers.
5. Network DBMS, where data is stored in a network format enabling relationships between records.

4. What is SQL?

SQL or Structured Query Language is used as a tool to interact with databases. It provides capabilities such as retrieving information, adding new records, updating or removing existing ones as well as altering database structures, and managing user access rights.

5. What is normalization and why is it important?

Normalization is the process of organizing data in a database. It includes creating related tables based on rules. Normalization is important as it helps reduce repetitiveness in the data and ensures that it remains consistent.

6. What is a primary key?

A primary key helps to identify each row uniquely by ensuring that no two rows have the same values. Every row has a unique primary key column or columns.

CREATE TABLE Students (
    StudentID INT PRIMARY KEY,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    Age INT
);

Here, 'StudentID' is the primary key column for the table 'Students'.

7. What is a foreign key?

A foreign key is a column or a group of columns in a table that refers to the primary key of another table. It binds such tables together where the set of values in the column of the foreign key of one table is the same as the values in the columns of the primary key of another table.

CREATE TABLE Customers (
    CustomerID int PRIMARY KEY,
    Name varchar(255)
);

CREATE TABLE Orders (
    OrderID int PRIMARY KEY,
    CustomerID int,
    OrderDate datetime,
    FOREIGN KEY (CustomerID) REFERENCES Customers(CustomerID)
);

Here, the 'Customers' table has a primary key as 'CustomerID', and the 'Orders' table has a primary key as 'CustomerID' and a foreign key as 'CustomerID'.

8. What is the difference between primary key and unique constraints?

9. What is a super key?

A super key is a set of attributes on which the other attributes are dependent for functions.

10. What is a Trigger?

When a table is operated on, a trigger is a script that automatically runs. Methods include insert, update, and delete.

CREATE TRIGGER UpdateLastOrderDate
ON Orders
AFTER INSERT
AS
BEGIN
    UPDATE Customers
    SET LastOrderDate = GETDATE()
    WHERE CustomerID IN (SELECT CustomerID FROM inserted)
END;

11. What is the difference between Trigger and Stored Procedure?

The main difference between Triggers and Stored Procedures is that triggers can only be attached to queries in order to be executed. Unlike triggers, stored procedures can be called directly.

12. What are indexes?

Indexes enable the user to locate data without the need to search every row in a database table, allowing data to be accessed easily anytime when required. This improves the speed of operations for accessing data in a database.

13. What is Denormalization?

Denormalization is performed on a previously normalized database to increase its performance. It is a method of boosting efficiency by introducing repetitive data into one or more tables.

14. What is the full form of ACID in DBMS?

In DBMS, ACID stands for Atomicity, Consistency, Isolation, and Durability. These are the four properties that make DBMS transactions more reliable and correct.

15. What is a database schema?

A database schema is similar to a blueprint for organizing information in a database. It groups the database objects and displays them as tables, functions, etc.

16. What is data redundancy, and how does normalization help to reduce it?

Data redundancy refers to the repetition of data. This repetition of data can sometimes lead to a lack of consistency in data and irregularity in a database. Normalization helps to reduce data redundancy by storing data only once and eliminating duplicate information. It also helps minimize dependency by dividing large tables into smaller ones making them more manageable.

17. What is the difference between a database and a DBMS?

A database is an organized collection of data, while a DBMS (Database Management System) is software used to manage, manipulate, and interact with databases. In other words, a database is a container for storing data, while a DBMS provides the tools and functionalities to manage that data.

18. What are the main components of a DBMS?

The main components of a DBMS include:

• Data Definition Language (DDL): Used to define the structure and schema of the database.
• Data Manipulation Language (DML): Used to perform operations such as querying, inserting, updating, and deleting data.
• Data Control Language (DCL): Used to control access to the database and manage user permissions.
• Transaction Control: Ensures that transactions are executed reliably and consistently.
• Query Processor: Interprets and executes SQL queries.
• Storage Manager: Manages the storage of data on disk and in memory.

19. What is a transaction in DBMS?

A transaction is a logical unit of work that consists of one or more database operations, such as reading or writing data. Transactions make sure that everything stays in order. If the transaction occurs smoothly, the changes are made part of the database, but if not, it restores back to how it was.

20. What is the purpose of SQL?

SQL is a short form for Structured Query Language. The main purpose of SQL is to interact with the relational databases. The interactions may be like processes of inserting, removing, or updating the data in the database.

21. What are views used for?

The various uses of views are:

• They create a virtual table after joining and simplifying multiple tables into one.
• They can also be used to hide the complexity of the data.
• They need less storage as only the definition of the view is stored in the database not the copy of all the related data.
• Views provide extra security based on the SQL engine being used.

22. What are clustered and non-clustered Indexes?

• Clustered Indexes-These indexes determine how the data is physically stored on a disk.
• Non-Clustered Indexes-These are indexes that determine the logical ordering of the data.

23. Explain the ACID properties in the context of DBMS.

There are four ACID properties in DBMS:

1. Atomicity-This property makes sure that a transaction is treated as a single, individual unit of work.
2. Consistency- This property keeps a check on the state of the database before and after the transaction to ensure it stays consistent.
3. Isolation-This property is to ensure that two transactions executing at the same time do not interfere with each other.
4. Durability-This property ensures that even if there is a system failure, the effects of the transaction are there.

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

There are mainly three types of relationships in a relational database:

1. One-to-One Relationship- Each record in one is related to exactly one record in another table.
2. One-to-Many Relationship- Each record in one table can be related to multiple records in another. Still, each record in the second table is related to only one record in the first table.
3. Many-to-Many Relationship-Multiple records in one table can be related to multiple records in another table.

25. What is the concept of sub-query in terms of SQL?

A sub-query is also known as an inner query present in another query. These are the queries that are present inside some other query, also known as an outer query.

SELECT Name
FROM Employees
WHERE DepartmentID = (
    SELECT DepartmentID
    FROM Departments
    WHERE DepartmentName = 'Sales'
);

DBMS Interview Questions and Answers for Intermediate

26. Explain the different levels of data abstraction in a DBMS.

In DBMS, there are three levels of data abstraction:

1. Physical Level-It describes how data is stored on the storage medium.
2. Logical Level-It describes the logical structure of the entire database, which includes tables, columns, relationships, and constraints.
3. View Level- It describes the way users perceive the data, allowing them to access a subset of the database through views, which are virtual tables derived from one or more base tables.

27. What is a heap table?

Heap tables are unordered tables where data is stored in an unorganized manner. They are stored as a heap. When the data is received into the table, it is inserted as it is and sent to the next data page available.

28. What is the difference between a heap table and a clustered table in a DBMS?

29. What are the various forms in normalization?

Database normalization is the process where the data is organized in a database in a series of normal forms. This helps in reducing redundancy and dependency which in turn, improves the data integrity. The various normal forms are as follows:

1. First Normal Form (1NF)
2. Second Normal Form (2NF)
3. Third Normal Form (3NF)
4. Boyce-Codd Normal Form (BCNF)
5. Fourth Normal Form (4NF)
6. Fifth Normal Form (5NF)
7. Sixth Normal Form (6NF)

30. What is a deadlock in a DBMS, and how can it be prevented?

A deadlock is a situation that occurs in a DBMS where two or more transactions are waiting continuously for each other so as to when they will release the locks on resources. This situation results in a condition where no transaction is proceeding further indefinitely. These kinds of situations can be prevented with the help of a few techniques such as:

• Deadlock Detection
• Timeout Mechanisms
• Deadlock Avoidance Algorithms
• Deadlock Prevention Strategies.

31. Explain the concept of database transaction isolation levels

The transaction isolation levels are the ones that tell about the degree to which the transactions are isolated from each other. There are mainly three types of isolation levels that are:

• Read Uncommitted
• Read Committed
• Repeatable Read
• Serializable

32. What are database constraints?

Database constraints are some of those rules that ensure that the data in a database stays in order. It puts restrictions on the values that can be stored in columns or tables. Common types of constraints include primary key, foreign key, unique, not null, check, and default constraints. Constraints ensure that the data is following some set of specified rules. It makes sure that no incorrect or invalid data in inserted in the database.

33. What is the difference between a database trigger and a stored procedure?

• Database Trigger: A database trigger is a special type of stored procedure that automatically executes in response to specific events, such as INSERT, UPDATE, or DELETE operations on a table. Triggers are associated with a specific table and are executed implicitly when the triggering event occurs.
• Stored Procedure: A stored procedure is a precompiled SQL script that is stored in the database and can be executed explicitly by a user or application. Unlike triggers, stored procedures are not associated with specific events and must be called explicitly to execute.

34. What is a database index, and how does it work?

A database index is a data structure that helps in finding specific rows in a table easily and quickly. Indexes are created on one or more columns of a table and store references to the physical location of data rows. When a query is executed, the DBMS uses the index to quickly locate the relevant rows based on the search criteria specified in the query.

35. Explain the concept of database replication and its benefits.

Database replication is the process where data is copied and its identical copies are kept on multiple servers. Replication can be synchronous or asynchronous and can serve various purposes, including:

• Improved fault tolerance and high availability
• Load balancing and scalability
• Disaster recovery and backup
• Geographic distribution of data for distributed applications

36. How are database transactions managed in a DBMS?

A database transaction is a logical unit of work that consists of one or more database operations, such as reading from or writing to the database. When transactions make changes, they update the database, but if an error occurs, it reverts back to its previous state. The DBMS manages transactions through mechanisms such as transaction logs, concurrency control, and recovery techniques.

37. What is database sharding, and how does it improve scalability?

Database sharding is a technique used to horizontally partition a large database into smaller, more manageable pieces called shards. Each shard contains a subset of the data and is stored on a separate server. Sharding distributes the workload on multiple servers which helps in improving scalability and queries and transactions can occur simultaneously.

38. What is the difference between a view and a materialized view?

• View: A view is a virtual table derived from one or more base tables. It does not store data physically but provides a logical representation of the data. Views are dynamically generated at the time of query execution.
• Materialized View: A materialized view is a physical copy of the result set of a query stored as a table. Unlike views, materialized views store data physically and are updated periodically to synchronize with the base tables. Materialized views improve query performance by precomputing and storing the results of expensive queries.

39. What is database concurrency control, and why is it important?

Database concurrency control is the process of managing simultaneous access to the database by multiple users or transactions. It ensures that there is consistency in a multi-user environment and that no operations interfere with each other on the database. Some of the commonly used concurrency control techniques are:

• Locking
• Optimistic concurrency control
• Multi-version concurrency control.

40. What is database partitioning, and how does it improve performance?

Database partitioning is the process of dividing a large database table into smaller, more manageable segments called partitions. Each partition contains a subset of the data and can be stored on separate storage devices or servers. Partitioning improves performance by distributing the data and workload across multiple disks or servers, so the transactions and queries can be processed parallely.

DBMS Interview Questions and Answers for Experienced

41. Explain the concept of database locking and the different types of locks used in a DBMS.

Database locking is a mechanism used to control concurrent access to data by multiple users or transactions. Different types of locks include:

• Shared Lock (S-lock): Allows multiple transactions to read a resource concurrently but prevents any transaction from writing to it.
• Exclusive Lock (X-lock): Prevents other transactions from reading or writing to a resource until the lock is released.
• Intent Lock: Indicates the intention of a transaction to acquire a certain type of lock on a resource.
• Schema Lock: Locks the schema of a database object, preventing other transactions from altering its structure.

42. When is it appropriate to denormalize a database?

Database denormalization is the process of intentionally introducing redundancy into a database schema to improve performance or simplify query processing. Denormalization is appropriate in scenarios where:

• There are performance bottlenecks due to frequent joins or complex queries.
• The database is read-heavy, and optimizing for read operations is a priority.
• The application requirements change frequently, making it impractical to maintain a highly normalized schema.

43. Explain the concept of database indexing, and discuss the factors that influence the choice of index type.

Database indexing is a technique used to improve the speed of data retrieval operations by creating data structures (indexes) that store references to the location of data in the database. Factors influencing the choice of index type include:

• Selectivity of the indexed column(s)
• Cardinality of the indexed column(s)
• Query patterns and access patterns
• Write performance considerations
• Storage space requirements

44. Discuss the challenges and strategies for database performance tuning in a large-scale production environment.

Database performance tuning in a large-scale production environment involves addressing various challenges, including:

• Identifying and resolving performance bottlenecks
• Optimizing query execution plans
• Tuning indexing strategies
• Managing database configuration parameters
• Scaling the database infrastructure horizontally or vertically
• Strategies for performance tuning include:
• Analyzing query execution plans and optimizing SQL queries
• Implementing appropriate indexing strategies
• Partitioning large tables to distribute the workload
• Utilizing caching mechanisms to reduce database load
• Regular monitoring and performance testing

45. What is database replication and what are its different replication models?

Database replication is the process where data is copied and kept as identical copies on multiple servers. Different replication models include:

• Master-Slave Replication
• Master-Master Replication
• Peer-to-Peer Replication
• Multi-Master Replication with Conflict Resolution
• Replication models differ in terms of data consistency, scalability, and fault tolerance characteristics.

46. What are database materialized views, and how do they differ from regular views?

• Materialized View: A materialized view is a physical copy of the result set of a query stored as a table. Materialized views store data physically and are updated periodically to synchronize with the base tables. They improve query performance by precomputing and storing the results of expensive queries.
• Regular View: A regular view is a virtual table derived from one or more base tables. It does not store data physically but provides a logical representation of the data. Views are dynamically generated at the time of query execution.

47. Discuss the concept of database concurrency control, and explain how it is implemented in a multi-user environment.

Database concurrency control is the process of managing simultaneous access to data by multiple users or transactions. It ensures that transactions execute correctly and consistently in a multi-user environment by preventing conflicts and maintaining data integrity. Concurrency control is implemented through techniques such as locking, optimistic concurrency control, and multi-version concurrency control.

48. What are database triggers, and how can they be effectively used to enforce business rules and data integrity constraints?

Database triggers are special types of stored procedures that automatically execute in response to specific events, such as INSERT, UPDATE, or DELETE operations on a table. Triggers can be effectively used to enforce business rules and data integrity constraints by:

• Validating data before it is inserted, updated, or deleted in the database
• Enforcing referential integrity and cascading updates or deletes across related tables
• Auditing changes to the database for compliance and security purposes
• Implementing custom business logic and complex data validation rules

49. Explain the concept of database sharding, and discuss its benefits and challenges in distributed database systems.

Database sharding is a technique used to horizontally partition a large database into smaller, more manageable pieces called shards. Each shard contains a subset of the data and is stored on a separate server. Benefits of database sharding include:

• Improved scalability and performance by distributing the workload across multiple servers
• Enhanced fault tolerance and availability
• Flexibility in data placement and management
• Challenges of database sharding include:
• Complexity of data distribution and routing
• Increased overhead of managing distributed transactions and consistency
• Potential for data skew and imbalance among shards

50. Discuss the concept of database materialized views, and provide examples of scenarios where they can be beneficial in improving query performance.

A materialized view is a physical copy of the result set of a query stored as a table. Materialized views store data physically and are updated periodically to synchronize with the base tables. They improve query performance by precomputing and storing the results of expensive queries. Materialized views can be beneficial in scenarios where:

• Complex queries involving joins and aggregations need to be executed frequently.
• Query performance needs to be optimized for read-heavy workloads.
• Data from multiple tables needs to be aggregated or summarized for reporting purposes.
• Query response times need to be reduced, especially in decision support systems and analytical applications.

Summary

Hope this comprehensive guide to the most important DBMS interview questions helped you review as well as increase your knowledge in DBMS. To learn more about different concepts of it in detail, consider enrolling in our SQL Server Course.