Top 50 DMBS Interview Questions Answers

In this article, we will discuss the top 50 DBMS interview questions frequently asked by hiring managers.

As the world becomes increasingly data-driven, the importance of Database Management Systems (DBMS) has grown significantly.

DBMS is a software system that allows users to manage and organize data in a structured and accessible way.

If you’re seeking a job in the field of database management, it’s important to be prepared for interviews by studying common DBMS interview questions and answers.

In this article, we will discuss some of the top 50 DBMS interview questions that are frequently asked by hiring managers and provide answers that will help you stand out from the competition.

Whether you’re a seasoned database professional or just starting out, these questions will give you a better understanding of the skills and knowledge required to succeed in this field.

Here’s the list of the Top 50 DBMS questions with answers.

[Q1] What is DBMS?

• A DBMS, or Database Management System, is a software system that allows users to store, retrieve, manage, and manipulate data in a database. It is a software system designed to manage and organize large amounts of information in a structured and accessible way. DBMS software is used to create, manage, and maintain databases of various types, including relational databases, object-oriented databases, and XML databases.

• A DBMS typically includes tools for data entry, data retrieval, data manipulation, and data analysis. It also includes features for managing database security, backup and recovery, and database performance tuning. With a DBMS, users can create tables, define relationships between tables, and query the database to retrieve specific data.

• Some popular examples of DBMS software include Oracle, Microsoft SQL Server, MySQL, PostgreSQL, and MongoDB.

[Q2] Mention some advantages of using DBMS.

• DBMS is a structure that manages and handles large volumes of data stored in a database. 
• It serves as an intermediate between users and the database. 
• The benefits of using a DBMS include improved data sharing and data security, increased data consistency and integrity, efficient data access and retrieval, and better decision-making based on accurate and up-to-date information.
• The following are a few advantages of a database management system-
  • Data redundancy- this happens when multiple copies of data are stored. With DBMS, data is stored in one structure database and the data is inputted only once.
  • No unauthorized access- it discourages unauthorized access and improves data access.
  • Supports multiple user interfaces.
  • Minimized data inconsistency- In DBMS, data inconsistency is reduced as different versions of the same data don’t appear in different places.

[Q3] What are the features of Database language?

• Database language is used to create and store data in computer systems. 
• DBMS itself is one of the features of database language which is a software application for the management of data. 
• Database language also facilitates the modification and alteration of query results by averaging, counting, summing, etc. 
• Database language enables user’s interact with other applications.

[Q4] How many types of database languages exist?

There are four types of Database language, i.e. DDL, DML, DCL, and TCL which are used for reading and updating data in a Database.

• DDL– Data Definition Language which includes CREATE, ALTER, and DROP.
• DML– Data Manipulation Language which includes SELECT, UPDATE, INSERT, etc.
• DCL– Data Control Language which consists of GRANT and REVOKE.
• TCL– Transaction Control Languages such as COMMIT and ROLLBACK.

[Q5] What is normalization, and why is it important in database design?

Normalization is the process of organizing data in a database to reduce data redundancy and improve data integrity.

It involves breaking down a database into smaller, more manageable tables and defining relationships between those tables.

Normalization is important in database design because it reduces data duplication, minimizes data inconsistencies, and improves database performance.

[Q6] What is database normalization? Explain the types of it.

• In SQL, the normalization of data is a process through which data is organized in tables used for the reduction of redundancy and dependency on data. 
• It divides large tables into smaller ones using some set of rules.
• Types of normalization:
  • 1NF: The rules of 1NF are that each table must contain a single value and records are required to be unique.
  • 2NF: The rules of 2NF are that the table must be in 1NF and must possess a single-column primary key.
  • 3NF: The rules of 3NF are that the table must be in 2NF and must not have any transitive functional dependencies.
  • BCNF: The rules of the Boyce Codd Normal form is that it must be in 3 NF and must not have more than one candidate key.

[Q7] What is the difference between a primary key and a foreign key?

• A primary key is a column or combination of columns in a table that uniquely identifies each row in the table.

• A foreign key is a column or combination of columns in one table that refers to the primary key in another table. The foreign key establishes a relationship between the two tables.

[Q8] What is a join in SQL, and what types of joins are there?

A join in SQL combines data from two or more tables based on a related column between them.

The types of joins include inner join, left outer join, right outer join, and full outer join.

[Q9] What are the different types of joins, and how do they work?

There are several types of joins in DBMS, including inner join, left join, right join, and full outer join.

• An inner join returns only the rows that have matching values in both tables.

• A left join returns all rows from the left table and matching rows from the right table.

• A right join returns all rows from the right table and matching rows from the left table.

• A full outer join returns all rows from both tables, with matching rows combined.

[Q10] What is a self-join, and when is it used?

A self-join is a join operation in which a table is joined with itself.

It is used to retrieve related data from the same table, such as when a table has a hierarchical structure or when you need to compare records within the same table.

[Q11] What is a cross join, and when is it used?

A cross join is a join operation that returns the Cartesian product of two tables, meaning all possible combinations of rows from both tables.

It is used when you need to create a list of all possible combinations of items from two or more tables.

[Q12] What is the difference between an inner join and an outer join?

The main difference between an inner join and an outer join is that an inner join returns only the rows that have matching values in both tables,

An outer join returns all the rows from at least one table, including those that have no matching values in the other table.

[Q13] What is a natural join, and how is it different from an equijoin?

A natural join is a join operation that matches columns in two tables with the same name and data type. It is different from an equijoin because it automatically determines the join condition based on the columns with the same name in both tables.

[Q14] What is a non-equijoin, and when is it used?

A non-equijoin is a join operation that uses operators other than equals to join two tables, such as greater than or less than.

It is used when you need to join tables based on non-matching values.

[Q15] What is a theta join, and when is it used?

A theta join is a join operation that uses comparison operators other than equals to join two tables, such as greater than or less than.

It is used when you need to join tables based on non-matching values.

[Q16] What is a semi-join, and when is it used?

A semi-join is a join operation that returns only the rows from one table that have matching rows in the other table.

It is used when you need to retrieve data from one table based on the existence of matching data in another table.

[Q17] What is a view in a database, and what are the advantages of using views?

• A view in a database is a virtual table that is based on the result of a SELECT statement.

• The advantages of using views include simplifying complex queries, improving performance, enforcing security, and providing a logical data model.

[Q18] Explain triggers in a database, and how are they used.

• A trigger in a database is a set of actions that are automatically executed in response to a specific event or change in the database.

• Triggers are used to enforce data integrity, perform complex calculations, and automate tasks in a database.

[Q19] What is ACID, and why is it important in database transactions?

• ACID stands for Atomicity, Consistency, Isolation, and Durability, and it is a set of properties that ensure reliable database transactions.
• Atomicity ensures that all parts of a transaction are executed or none of them are.
• Consistency ensures that a transaction brings the database from one valid state to another.
• Isolation ensures that concurrent transactions do not interfere with each other.
• Durability ensures that once a transaction is committed, its changes are permanent.

[Q20] What is a stored procedure, and how is it used in a database?

• A stored procedure is a set of precompiled SQL statements that are stored in a database and can be executed on demand.

• Stored procedures are used to encapsulate business logic, improve performance, and enforce security in a database.

[Q21] What is a data warehouse, and how is it different from a database?

• A data warehouse is a large, centralized repository of data that is used for business intelligence and decision-making.

• It is different from a database in that it is optimized for analytical queries rather than transaction processing.

[Q22] What is a NoSQL database, and when is it used?

A NoSQL database is a non-relational database that does not use the traditional tabular schema of a relational database.

NoSQL databases are used when scalability, flexibility, and performance are more important than data consistency and integrity.

[Q23] What is a database index?

• Many Information is stored in a database and locating and retrieving the information will be difficult without an index. 
• A database index is, therefore, that which makes searching and retrieving specific data or information from a database easier and faster. 
• A database index can be likened to an old recipe box that has dividers. 
• Through the recipe box, you are directed to various categories such as cereals, legumes, salads, soups, and vegetables. 
• Instead of searching through all the numerous categories, a database index takes you directly to what you are looking for. 
• The science catalog in an online library is another example of a database index.
  

[Q24] Why is indexing in a database important?

An index in DBMS is a database object that helps in faster data retrieval.

Indexing is the process of creating a data structure that improves the speed of data retrieval operations in a database. Indexing is important because it enables faster queries, reduces disk I

It works by creating a separate data structure that contains the indexed data and pointers to the actual data in the table.

[Q25] What are the different types of indexes in DBMS?

The different types of indexes in DBMS include B-tree indexes, hash indexes, bitmap indexes, and clustered and non-clustered indexes.

[Q26] What is the difference between clustered and non-clustered indexes?

A clustered index determines the physical order of data in a table, while a non-clustered index is a separate data structure that contains a copy of the indexed data and pointers to the actual data in the table.

[Q27] What is a composite index, and when is it used?

A composite index is an index that contains multiple columns. It is used when you need to retrieve data based on multiple criteria, and the composite index can improve the performance of such queries.

[Q28] What is the purpose of an index in a database?

The purpose of an index in a database is to speed up data retrieval.

An index allows the database engine to quickly locate the data without having to scan the entire table.

[Q29] What is the difference between a unique index and a primary key?

A unique index and a primary key both enforce the uniqueness of values in a column or set of columns.

The primary key is a special type of unique index that is used to uniquely identify a row in a table. A table can have only one primary key, while it can have multiple unique indexes.

[Q30] What is the difference between a clustered index and a non-clustered index?

A clustered index determines the physical order of data in a table, while a non-clustered index is a separate data structure that contains a copy of the indexed data and pointers to the actual data in the table.

[Q31] What is an index scan, and how is it different from an index seek?

An index scan is a query execution plan that involves scanning the entire index to retrieve the data.

An index seek is a query execution plan that uses the index to locate the data quickly without scanning the entire index.

[Q32] What is a covering index, and when is it used?

A covering index is an index that contains all the columns required to satisfy a query, so the query can be resolved entirely from the index without accessing the actual data in the table.

It is used when you need to optimize queries that require multiple columns.

[Q33] What is the purpose of a partial index, and when is it used?

A partial index is an index that contains a subset of the rows in a table. It is used to optimize queries that require only a subset of the data in the table, and can improve query performance by reducing the size of the index.

[Q34] List a few disadvantages of the File processing system.

• The file processing system is inconsistent and insecure. 
• There are also chances of data redundancy and duplication. 
• Sometimes, it gets difficult to access data and concurrent access is also not supported. 
• There is a scope for data isolation and integrity.

[Q35] Enlist various types of interactions created by DBMS.

• There are various kinds of interactions supported by DBMS-
  • Data definition
  • Update
  • Retrieval
  • Administration

[Q36] What are the different relationships existing in the database?

A relationship in the database is established when one table has a foreign key that references the primary key of another table.

There are three relationships existing between databases

• One-to-one– This simple relationship exists among two tables having the same rows or columns.
• One-to-many– Two tables connected by a foreign key and a primary key enjoy a one-to-many relationship.
• Many-to-many – It is a complex relationship in which many records in one table are connected to many records in another table.

[Q37] State some commands of DDL in DBMS.

DDL commands are used to modify and edit the structure of a database system. Some of the important commands are-

• CREATE table command- It defines each column of the table in a unique and distinct manner like name, data type, size, etc.
  Syntax: CREATE TABLE [column name] ([column definitions]) [table parameters]
• ALTER table command- ALTER is used to make changes and edit the existing table of the database. Syntax: ALTER objecttype objectname parameters.
• DROP table command – DROP is used for destroying a table and all the recorded data in it. It destroys an existing database.  
  Syntax: DROP objecttype objectname parameters.

[Q38] What are the different cursor types in DBMS?

A database cursor enables traversal over the records in the database. The different cursor types are-

• Dynamic – it is highly subject to changes while scrolling the cursor in the database.
• Static – it doesn’t show any changes while scrolling. It also works on the recording of snapshots.
• Keyset – it enables the user to modify the data without displaying the new data.

[Q39] Enlist the types of the cursor.

There are two types of Cursor in SQL-

• Implicit cursor– Implicit cursors are automatically created whenever an SQL statement is executed and this happens without the user’s notice.
• Explicit cursor– Explicit cursors are created with the awareness of users. It handles the SQP/PL query in one row and exercises more control over the context area.

[Q40] List a few restrictions that are imposed while creating views.

• There are certain restrictions that are applied while creating views in the database-
  • Only the current database can have views. 
  • No other database is allowed to have views other than the current database.
  • You cannot make any changes in the computed values of any view.
  • You cannot apply full-text index definitions.
  • Temporary views cannot be created and temporary tables cannot have views.
  • It is not associated with any default definitions.
  • There are integrity constants that define the working of commands such as insert and delete.
  • Triggers such as INSTEAD is associated with views.

[Q41] How index hunting contributes to improving query performance?

• Index hunting is viewed as an important part of the database management system. 
• It enhances the speed and the query performance of the database. 
• It is done in the following ways-In order to coordinate the study of a query with the workload, the query optimizer is used. 
• It also suggests the best use of queries based on the optimizer.
• The performance of query distribution is checked and monitored to know their effects.
• Turning complex databases into small chunks of queries is also suggested.

[Q42] Mention some disadvantages of the query.

• There are a few disadvantages of query –
  • There are no indexes in the query.
  • Triggers and procedures are SET NOCOUNT ON.
  • Sometimes joins that are complicated and complex are excessively complied.
  • Cursors and tables that are temporary depict a bad presentation.

[Q43] List a few ways to code transactions in an efficient manner.

• It is imperative that transactions are kept as short as possible. 
• It should be short in order to reduce contention for resources. 
• The following are a few guidelines for coding transactions efficiently –
  • It doesn’t require input from users during transactions.
  • Transactions must not be opened while browsing through data.
  • Make use of lower transaction levels.
  • While transacting, the least information of data must be accessed

[Q44] Differentiate between Nested loop, Hash loop, and Merge Join.

• Nested loop- A nested loop is a loop within a loop. It is an inner loop within an outer body that allows fewer entries. Individual entries in a nested loop are processed individually in the inner loop
• Hash join- it is divided into-
  • Build- this hash table has in-memory which is present on the smaller table.
  • Probe – it is the hash value present in each second-row element.
  • Sort merge element- it joins two independent sources of data.
  • It is considered a better option as compared with a nested loop when the data volume is big

[Q45] What is the importance of partitioning in DBMS?

• Database partitioning is the process of splitting large tables into smaller database entities. 
• The following are the benefits of partitioning-
  • When rows are in one partition, query performance in such situations is improved.
  • It also helps to access large parts of a single partition.
  • Data that are rarely used can be stored in slower and cheaper storage mediums.

[Q46] Define Atomicity and Aggregation.

• Atomicity: In database management, atomicity is a concept that assures the users of incomplete transactions. It takes care of these transactions and the actions related to incomplete transactions are left undone in DBMS.
• Aggregation: It aggregates the collected entities and their relationships. In this, information is gathered and expressed in summary form.

[Q47] Enlist various transaction phases.

There are three main transaction phases in the database which include

• Analysis phase
• Redo phase
• Undo phase.

 [Q48] What is a checkpoint in DBMS?

• In DBMS, the checkpoint is a type of mechanism where all the previous logs are removed from the system and permanently stored in the storage disk. 
• When it reaches the checkpoint, then the transaction will be updated in the database, and to that point, the entire log file will be removed from the file.

[Q49] What is recovery in DBMS, and why is it important?

Recovery in DBMS refers to the process of restoring a database to its previous state after a failure.

It is important because it ensures the integrity and consistency of data, and prevents data loss or corruption.

[Q50] What are the different types of recovery in DBMS?

The different types of recovery in DBMS include:

• Restart recovery
• Rollback recovery
• Forward recovery

[Q51] What is the difference between restart recovery and rollback recovery?

Restart recovery involves restarting the database from a known good state, while rollback recovery involves undoing transactions that were in progress when a failure occurred.

Restart recovery is typically used for catastrophic failures, while rollback recovery is used for more minor failures.

[Q52] What is the purpose of a transaction log in DBMS recovery?

A transaction log is used to record all changes made to the database, including updates, inserts, and deletes.

The log is used during recovery to undo any incomplete transactions that were in progress when a failure occurred.

[Q53] What is a checkpoint in DBMS recovery, and how does it work?

A checkpoint is a point in time when the database is in a consistent state, with all changes up to that point written to disk.

Checkpoints are used during recovery to reduce the amount of work required to restore the database to a consistent state.

[Q54] What is forward recovery in DBMS, and when is it used?

Forward recovery involves applying all committed transactions to the database after a failure. It is used when it is not possible to restart the database from a known good state or undo incomplete transactions.

[Q55] What is the difference between a full backup and an incremental backup in DBMS recovery?

A full backup involves backing up the entire database, while an incremental backup only backs up changes made since the last backup.

Full backups are typically used for major recovery efforts, while incremental backups are used for more frequent backups to minimize data loss.

[Q56] What is a recovery point objective (RPO) in DBMS recovery, and how is it determined?

A recovery point objective is the amount of data loss that is acceptable during a recovery effort.

It is determined by the business requirements and the data management policies of an organization.

[Q57] What is a recovery time objective (RTO) in DBMS recovery, and how is it determined?

A recovery time objective is the maximum allowable downtime during a recovery effort.

It is determined by the business requirements and the service level agreements of an organization.

[Q58] What is a database snapshot in DBMS recovery, and how is it used?

A database snapshot is a read-only copy of the database that can be used to recover data to a previous state.

It is used during recovery to quickly recover to a known good state without having to perform a full restore from a backup.