A database is a structured collection of data that is organized, stored, and managed for easy access, retrieval, and manipulation. It serves as a central repository for storing and managing various types of data, allowing users to efficiently store, retrieve, update, and analyze information for various purposes. Let’s understand top database interview questions with answers.
Databases have evolved over the years, and database management systems are now widely used by organizations. With DBMS, organizations can increase their accessibility to data and share data quickly and effectively. Database systems are important for any company that wants to secure or process data to get valuable information. Suppose you are planning to prepare for your upcoming Database interview. In that case, this article will boost your interview preparation by providing the top DBMS interview questions that an interviewer could ask you during your next interview.
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Top Database Interview Questions & Answers
As per the U.S. Bureau of Labor Statistics, the “employment of database administrators is projected to grow 10 percent from 2019 to 2029.”
There are a lot of opportunities in various industries for database professionals who are willing to learn new things and can analyse, manage, and secure data. To help you clear your next database interview, we have curated a list of the most commonly-asked DBMS interview questions:
Gain in-depth knowledge of Databases, read our post – What is Databases?
Q1. What is DBMS?
Ans. Database Management System (DBMS) is a collection of programs that enables users to store, retrieve, update, and delete information from a database.
Q2. What is RDBMS?
Ans. A Relational Database Management system (RDBMS) is a type of DBMS based on the relational model. One can access or reassemble the data from the relational databases in many different ways without reorganising the database tables.
Q3. What is a ‘record’ in a database?
Ans. A ‘record’ is the collection of values/fields of a specific entity.
Q4. What is a ‘field’ in a database?
Ans. A ‘field’ is an area within a record reserved for a specific piece of data.
Q5. What are database languages? What are the types?
Ans. Database languages are used to write or create a database management system. There are three types: data definition language, data manipulation language, and query language.
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Q6. Name the various relationships of the database. Describe briefly.
Ans. The various relationships of the database are:
- One-to-one: Single table having drawn a relationship with another table with similar columns.
- One-to-many: Two tables having primary and foreign key relations.
- Many-to-many: Junction table having many tables related to many tables.
Q7. What is ‘normalization’?
Ans. Organized data void of inconsistent dependency and redundancy within a database is called ‘normalization.
Q8. What are the different types of normalization?
Ans. The different types of normalization are – First Formal Form (1NF), Second Normal Form (2NF), and Third Normal Form (2NF).
Q9. What is the ‘primary key’?
Ans. A ‘primary key’ is a column whose values uniquely identify every row in a table. Primary key values can never be reused.
Q10. What is ‘denormalization’?
Ans. Boosting up database performance, and adding redundant data which in turn helps rid of complex data is called ‘denormalization’.
Let’s take a look at some more database interview questions and answers.
Q11. What conditions must be met for a field to be defined as a primary key?
Ans. The conditions are:
- No two rows can have the same primary key value.
- Every row must have a primary key value.
- The primary key field cannot be null.
- Value in a primary key column can never be modified or updated if any foreign key refers to that primary key.
Q12. What is a ‘composite key’?
Ans. A ‘composite key’ is a combination of two or more columns in a table that can be used to identify each row in the table uniquely.
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Q13. What is a ‘foreign key’?
Ans. A ‘foreign key’ is a field (or collection of fields) in one table that uniquely identifies a row of another table or the same table.
Q14. What is a ‘unique key’?
Ans. The unique key is the same as the primary, with the difference being the existence of null. The unique key field allows one value as a NULL value.
Q15. What is a ‘cursor’?
Ans. A cursor is a database object that helps manipulate data row by row, representing a result set.
Q16. What are the different types of cursors? Define
Ans. The different types of cursors are:
- Dynamic: it reflects changes while scrolling.
- Static: doesn’t reflect changes while scrolling and works on recording a snapshot.
- Keyset: data modification without reflection of new data is seen.
Q17. What is a ‘sub-query’?
Ans. A query contained by a query is called a sub-query.
Q18. What is a ‘view’?
Ans. The views are virtual tables. Unlike Tables that contain data, views contain queries that dynamically retrieve data when used.
Q19. What is a materialized view?
Ans. Materialized views are also a view but are disk-based. Materialized views get updates on a specific duration based on the interval specified in the query definition. It can be indexed.
Q20. Define ‘join’.
Ans. Joins help in explaining the relation between different tables.
These are some of the popular questions asked in a Database interview. Always be prepared to answer all technical skills, interpersonal, leadership, or methodology questions. If you are someone who has recently started your career in database management, you can enrol in a database certification course to get the techniques and skills required to be an expert in the field.
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Q21. Explain the meaning of the extension of an entity type.
Ans. An extension of an entity type is a collection of entities of a particular entity type grouped into an entity set.
Q22. Explain concurrency control.
Ans. Concurrency control is used to manage simultaneous operations in a database. It ensures that database integrity is not compromised. There are two approaches to concurrency control:
- Optimistic approach
- Pessimistic approach
Now, let’s move on to some more DBMS interview questions.
Q23. What are the advantages of DBMS?
Ans. The advantages of DBMS are:
- Restriction on unauthorized access
- Redundancy control as data is stored in a structured way
- Multiple user interfaces
- Backup and recovery for data
- Data consistency
- Easy accessibility
- Easy data extraction and data processing
Suggested read: What are the Advantages of DBMS?
Q24. Explain checkpoint.
Ans. A Checkpoint is a mechanism in which all the previous logs are eliminated from the system and permanently stored in the storage disk. It declares a point before which the DBMS was in a consistent state.
The log file is destroyed upon reaching the checkpoint, and its update is saved in the database. A new log will then be created with the upcoming execution operations of the transaction. It keeps updating until the next checkpoint. Such checkpoints are traced during transaction execution, and log files are created after execution.
Q25. What are the disadvantages of file processing systems?
Ans. The disadvantages of file processing systems are:
- Data redundancy and inconsistency
- Data accessing is not easy – different programs are needed to access data differently.
- Concurrent access anomalies
- Data could be stored in different formats, so it could be challenging to share
- Issues with concurrent access
- Use of many copies of the same data
- Data isolation
- Atomicity problems
Q26. Explain DBMS data abstraction. What are its different levels?
Ans. Data abstraction is hiding irrelevant information/details from users to ease user interaction with the database. The three levels of Data abstraction are:
- Physical Level: It is the lowest level of abstraction. It specifies how data is stored in memory. Data can be accessed through sequential or random access.
- Conceptual/Logical Level: This is the second-highest level of abstraction. It stores information in the form of tables. It specifies what data is stored and the relationship among those data.
- View Level: It is the highest level of data abstraction. At this level, users can only view a part of the database as rows and columns. It hides the details about storage and implementation from the users. You can also have multiple views of the same database.
Q27. What is Functional Dependency in DBMS?
Ans. Functional dependency refers to the relationship between two attributes, usually the non-key attributes and the primary key of a table. There are two types of functional dependency:
- Trivial – A → B has trivial functional dependency if B is a subset of A.
- Non-trivial – A → B has a non-trivial functional dependency if B is not a subset of A.
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Q28. What is the difference between extension and intension?
Ans. The intention of a database is the constant value. It is the description of the database or the schema, which will not change frequently and is specified during the database design phase. On the other hand, the extension or database snapshot of the database is the set of database values that populate the data structures. It refers to the data at a particular time. It may change frequently.
Let’s move on to some more database interview questions.
Q29. What is a Data Model?
Ans. Data models specify how the logical structure of a database is modelled. They offer conceptual tools for describing data, relationships, semantics, and constraints. Data models describe the relationship between the entities and their attributes. Some of the data models are:
- Hierarchical Data Model
- Network Model
- Entity-Relationship Model
- Relational Model
- Semi-Structured Data Model
- Object-Relational Data Model
- Object-Oriented Data Model
Q30. Explain correlated subquery.
Ans. Also known as a synchronized subquery, a correlated subquery is a query nested inside another query that relies on the outer query to return a value. Since it is correlated with a column of the outer query, it must be re-executed for each result row. Thus, during execution, the subquery is executed first and then the correlated query.
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Q31. Explain the Database transaction.
Ans. A database transaction (DB transaction) is a unit of work performed within a database management system – either completed as a unit or undone as a unit. Once the transaction is complete, the successful completion will reflect in the system or the transaction fails, and no change will be reflected. Database transaction processing helps maintain the integrity of the database.
Q32. What is query optimization? What are its benefits?
Ans. Query optimization is the execution plan for evaluating a query efficiently and at the least estimated cost. Since a single query can be executed through different methods and algorithms, query optimization helps by specifying the most efficient way to execute a given query by considering all the possible query plans.
The benefits of query optimization are:
- Reduces the system resources
- Reduces the time and space complexity
- Provide the correct output faster
Q33. Explain Relational Algebra.
Ans. Relational Algebra is a procedural query language. It has a set of operations for the relational data model. Using these operations, you can specify basic retrieval requests or queries. Relational Algebra takes instances of one or two relations as input and provides a new relation as output. It uses operators to perform queries and is carried out recursively on the relation. The intermediate results are also considered relations. This feature makes the algebra ‘closed’. Some of the fundamental operations of relational algebra are:
- set difference
Q34. Explain Relational Calculus.
Ans. Relational Calculus is a non-procedural query language. Instead of Algebra, it uses mathematical predicate calculus. It is not the same as differential and integral calculus in mathematics. It is rather based on a branch of mathematical logic known as ‘predicate calculus’.
The two types of relational calculus are:
- Tuple relational calculus
- Domain relational calculus
Q35. Explain Database Index and Index Hunting.
Ans. A database index is a data structure that improves the speed of data retrieval operations on a database.
The procedure of boosting the collection of indexes is known as Index hunting. It improves the speed and query performance of the database. It can be done by various methods, such as query optimization and query distribution.
Q36. What are integrity rules in DBMS?
Ans. Data integrity is crucial for maintaining the database. In DBMS, integrity rules are used to inform the DBMS about some constraints in the real world. The two types of integrity rules in DBMS are:
- Entity Integrity
- Referential Integrity
Q37. Explain VDL and SDL.
Ans. VDL stands for View Definition Language. It describes user views and their mapping to the conceptual schema. SDL is short for Storage Definition Language. It represents the mapping between two schemas.
Q38. What is the relationship between data independence and view?
Ans. View accounts for the logical data independence since growth and restructuring of the base table is not reflected in the views.
Q39. How to communicate with an RDBMS?
Ans. To communicate with RDBMS, we will have to use SQL (Structured Query Language). Using SQL, we can perform various tasks such as creating a table, inserting data into it, querying, updating data, and more.
Q40. What is the difference between a DELETE command and a TRUNCATE command?
Ans. The differences between DELETE and TRUNCATE commands are:
|Data Manipulation Language (DML) type.
|Data Definition Language (DDL) type.
|It deletes only those rows which have the WHERE clause.
|It removes all the rows from the table.
|This can be rolled back.
|This cannot be rolled back.
|The speed of execution is slow as it maintains a log.
|It is faster as it does not maintain a log.
|Delete uses a row lock to perform the function.
|Truncate uses a table lock to perform the function.
Q41. What are the criteria for fully functional dependency?
Ans. For fully functional dependency, the relation must meet the requirement of a functional dependency. ‘X’ and ‘Y’ will be fully functional dependent when removing any attribute from A indicates that the dependency no longer holds.
Q42. What are the ACID properties?
Ans. ACID stands for Atomicity Consistency Isolation Durability. ACID properties are the rules that need to be fulfilled by every transaction to maintain integrity. The ACID properties are:
- Atomicity: An indivisible series of database operations implies that all transactions occur and run to completion in one go or no execution occurs.
- Consistency: This property specifies the uniformity of data. It means that the database must be consistent before and after the transaction.
- Isolation: It means that multiple transactions can be executed simultaneously without interfering with each other.
- Durability: A successful transaction will be stored in the non-volatile memory and will not be affected by system failure.
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Database interview questions are crucial in assessing a candidate’s knowledge and expertise in managing and manipulating data. They test an individual’s understanding of database concepts, SQL queries, and data modelling, ensuring that the chosen candidate can handle complex data-related tasks and contribute effectively to the organization’s data management needs. Mastering these questions demonstrates proficiency and enhances one’s chances of securing a rewarding role in the ever-evolving world of data.
How can I start a career in the field of Databases?
You can start a career in the field of Database by following the below path: 1. Take online courses (various platforms like Coursera, Edx, and Udemy offer Database courses); 2. Learn SQL and Oracle; 3. Search online for case studies and practice cases to get hands-on experience; 4. Look for junior database developer roles; 5. Move into senior database jobs
What qualification do I need to become a database administrator?
While some entry-level database jobs may require candidates with database administrator associate degrees the more advanced and higher-level jobs require a bachelor's degree in database administration, management information systems, computer science, or a related field.
What skills do database administrators need?
Database administrators need these skills: Hard Skills: SQL; Oracle; Linux; Unix; Windows; HTML Soft Skills: Problem-solving; Communication; Organizational skills; Patience; Attention to detail.
What does a database administrator do?
A database administrator ensures that the databases run efficiently. They use specialized software to store and organize data. They also perform some other tasks, such as data extraction, transformation, loading, software maintenance, and database backup and recovery.
What is the future of database jobs?
Database management systems are widely used by organizations to increase organizational accessibility to data, which helps them to share the data quickly and effectively across the organization. It is crucial for any company that wants to secure its data or process it to get valuable information out of it. There are a lot of opportunities for database professionals who are capable of analyzing, managing, and securing data.