In today’s market, the amount of data being created every day is staggering. In 2018, Forbes reported that “2.5 quintillion bytes of data were being created daily.” Even more impressively, that amount was only set to grow – and it did.
By all accounts, that’s a lot of data. It’s practically impossible to process this much data on one’s own without assistance from technology.
That is the challenge Database Management Systems (DBMSs) seek to address by making data manageable.
Today, DBMS expertise is an invaluable asset that employers appreciate. Database management skills may also be essential in the line of work you’re interested in.
So, if your upcoming job-seeking efforts include DBMS, our list of DBMS interview questions is here to help you.
DBMS Expertise and Why it Matters?
Before we begin, let us briefly stress the importance of this skill. DBMS expertise is often necessary if you seek to become a database administrator, but that’s far from its only use or application.
For one, database management is becoming increasingly necessary, as Forbes noted.
2022 marketing trends illustrated this perfectly; AI, Chatbots, and sophisticated CRM solutions are steadily becoming the norm.
As such, this is not a hyper-specific skill to acquire. Instead, you may find yourself needing it in various other fields.
Second, and for similar reasons, it’s a valuable skill that employers appreciate. It’s thus a worthy addition to your CV and may come up more often than you think.
If you’re a digital entrepreneur, you’re likely interested in personal branding; your image and name recognition will directly inform how you can build your online presence.
In short, if you have doubts, we can safely say DBMS expertise will only grow in value over time. It may not be the most accessible skill to acquire, but it is well worth it.
Using This list
Finally, before we begin, please remember this list is only cursory. The subject of DBMS is too vast to cover here, and so are many individual questions.
As such, you may best use this list as a point of reference and resort to educational resources for specifics.
After all, this list assumes you’re somewhat familiar with the subject – if you’re preparing for interviews.
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9+1 DBMS Interview Questions:
Now, here we may break down questions into subsections for easier reading. Specifically, we’ll cover the primary questions across three levels; basic, intermediate, and advanced.
So, let’s begin.
Basic DBMS Interview Questions
Questions of this level will prove you have basic knowledge of DBMS. More challenging or more specific questions will typically follow these.
#1 What is DBMS, and what is RDBMS?
This fundamental question will require you to remember your definitions and provide them concisely.
A DBMS is a set of applications that allows for database creation and management. Through it, the user can store, access, and retrieve data as needed.
An RDBMS is a Relational Database Management System that serves the same purpose. Its difference and advantage lie in storing data in tables rather than files, which makes locating specific values easier.
Examples of DBMSs include:
- Microsoft Access
- Apache Cassandra
Of course, if any specific DBMSs are relevant to your interview, you may note them as needed.
#2 What are the advantages of DBMS?
This question, too, just needs you to remember the merits of database management via DBMS.
DBMS comes with many advantages, including the following:
- Data sharing, as multiple users can access a single database at once
- Data security, since DBMSs employ authentication and encryption tools
- Access restriction, limiting access to authorized individuals
- Data longevity, as DBMSs, allow for database backups and recoveries
- Data independence, as data structure modifications don’t compromise existing data
You will typically only need to mention a few advantages before the interview proceeds to the next question.
#3 What languages are present in DBMSs?
Still, on basic DBMS interview questions, this one will need you to remember the main DBMS languages.
- Data Definition Language (DDL) includes definitional commands like CREATE, RENAME, and ALTER.
- Data Manipulation Language (DML) includes commands to manipulate existing database data like INSERT, DELETE, and UPDATE.
- Data Control Language (DCL) includes user permission-related commands like GRANT.
- Transaction Control Language (TCL) includes transactional commands like COMMIT and SAVEPOINT.
Remember that you must follow-up questions on specific commands, so be prepared.
Intermediate DBMS Interview Questions
Next, questions of this level will begin to delve into specifics and require a more profound knowledge of DBMS.
#1 What is the ACID in DBMS?
That is an equally simple question requiring that you remember the ACID acronym.
The acronym stands for Atomicity, Consistency, Isolation, and Durability. Each component reflects an essential DBMS transaction quality:
- Atomicity; all data changes must be reflected in the whole database – or not at all
- Consistency; all data must remain consistent during and after a database transaction
- Isolation; no two ongoing transactions must affect one another
- Durability; data changes made by a transaction must persist
Depending on the interview, you may have to delve into specific examples of these qualities.
#2 What are NULL values, and are they the same as zero?
This trick question will have you define NULL values and how they differ from zero values.
In brief, the two represent distinctly different things. They should not be confused – and will paint a very unflattering picture if they are.
A zero value reflects a number; it is 0 of a given data point. In contrast, a NULL value represents a value that is
- Unavailable, or
- Not applicable
It is entirely different from saying “ROI” has a NULL value, meaning it’s currently unknown, and that it has a value of 0, meaning it’s known that there’s zero ROI.
#3 What is the Entity-Relationship (E-R) model?
This question will require a slightly lengthier answer as you define the terms and functions of the E-R model.
At its core, this model is a diagrammatic database design. It depicts real-world objects and their relationships, as the name suggests.
Terms to note and explain are:
- Entity; a real-world object that has a set of attributes as its characteristics
- Entity type; a collection of entities that share enough attributes to group into a type
- Entity set; a set of all entities present within a specific entity type
- Relationship; the relevant relationship between entities
You may then provide an example of the E-R model, which should be simple enough.
Advanced DBMS Interview Questions
Finally, these questions will require some notable expertise. For them, you’ll need to outline terms carefully and explain specific functions.
#1 What’s the difference between DELETE and TRUNCATE?
This is a relatively tricky question in that the two commands are not entirely dissimilar. Here, remember to delve into specific functional differences between the two.
In brief, the DELETE command:
- It deletes rows from tables
- Deletes rows specified by the WHERE clause
- It rolls back if necessary
- It is relatively slow since it maintains a log to lock the row
In contrast, the TRUNCATE command:
- Deletes complete table data
- Does not have a WHERE clause
- It cannot be rolled back, except in some cases – which are prone to data loss
- It is faster than DELETE since it doesn’t maintain a log and deletes a table at once
So, while the two are not entirely irrelevant, they have distinct and notable differences.
#2 What’s the difference between extension and intention?
Another question on specific terms: you’d need to define the two.
Intension, also known as Data Schema, is the effective description of a database. Its main characteristics are:
- It is defined during database design
- It should remain unchanged
- It represents a constant value, which is not time-dependent
In contrast, extension is the number of tuples present in a table at any instance. It is, in essence, a snapshot of the database at a specific time. As such:
- It is created during database management at specific needed times
- It is, by design, expected to change constantly
- It represents a changing value as tuples are produced, updated, or destroyed in a database
As you can see, confusion between the two hinges more on confusing their names than their functions.
#3 Can you explain normalization?
A tricky one among advanced DBMS interview questions, this one might need you to delve deeper into normalization types. But first, let’s start with the basics.
Normalization is a process of organizing data into multiple tables. Its goals and benefits include:
- Reduced redundancy
- Minimized insertion, deletion, and update distractions
- Better usage of disk space through data consolidation
- Better database integrity
However, the tricky part comes in remembering and defining the different normalization levels. You may be asked about them or want to bring them up to showcase your expertise.
In either case, as a reminder, these are:
- First Normal Form (1NF); is the simplest type of normalization, which primarily seeks to give each column an atomic, single value and remove duplicate columns from the same table.
- Second Normal Form (2NF); the second level of normalization, which ensures every non-prime attribute is entirely dependent on the primary key.
- The third Normal Form (3NF); is the third normalization level, ensuring no transitive functional dependency.
- Boyce & Codd Normal Form (BCNF); an advanced level of 3NF, BCNF cements functional dependencies. For example, if Y is a prime attribute and X->Y, X cannot be a non-prime attribute.
Crucially, you must remember that each level of normalization relies on the previous one. For example, a 3NF must satisfy all the criteria of a 2NF, which is, by definition, an advanced 1NF normalization.
#4 What is denormalization?
Finally, this one may be a follow-up to a question on normalization. It may also not require you to explain both; advanced DBMS interview questions don’t always follow such patterns.
The reason why it’s often a follow-up is that denormalization is a process that follows normalization. Denormalization is not neglecting to normalize but reversing the normalization process.
Denormalization reverses normalization by combining previously separated and normalized tables. As such:
- Denormalization is a database optimization technique
- It enables faster data retrieval
- It lets database managers avoid costly JOINs
As you can see, this question may require that you also define normalization. You may need to begin there, answer that question independently, and then build up to answering this one.
What other DBMS interview questions might I be asked?
Beyond these, you should answer various questions that showcase your expertise. For example, regardless of difficulty, you may be asked more technical questions like:
- Questions on the differences among more than two commands, such as how DROP differs from both TRUNCATE and DELETE
- SQL-based questions, such as defining SQL, defining SQL sub-queries, and defining CLAUSE in SQL
- SQL query-based questions, such as ones on writing queries for specific functions, under specific criteria, or with particular limitations
Such questions will often, but not exclusively, be advanced-level questions. Still, if your interview is not for a DBMS-heavy position, it will most likely be limited to basic and intermediate ones.
In addition, depending on your interview, you may be asked questions on specific DBMSs, such as Oracle or MySQL. In such cases, always remember to brush up on your particular DBMS and be prepared to showcase your expertise.
DBMS Interview Questions: Wrap UP!
In closing, there are a few too many DBMS interview questions to cover in a single article.
Covering every possible question was not the intent either; instead, it was to give you an overview of what a DBMS interview might look like and prepare you for the different levels of difficulty the questions may cover.
While brief, we hope you found this list helpful and informative. If it didn’t convince you of the value of DBMS expertise, we hope it helped outline just how useful it can be in the modern employment landscape.
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