Top DBMS Interview Questions You Need to Know

By Anvesha Jain 29-Jul-2022
Top DBMS Interview Questions You Need to Know

Data is a critical part of every domain, industry, and business today. About 2.5 quintillion data bytes get generated in a single day; this is more than all the data ever developed before 2002. Analyzing this information and deriving real-world insights from it is the fundamental purpose of this data. 

Global markets face increased demand for data professionals skilled in using database management systems. If you pick up this skill, you are on your way to becoming a professional database administrator.

However, to become a DBMS professional, you need hours of preparation to pass the certification exam and invest in practice to clear the interview. You cannot know what questions will be part of the interview, but you have a higher chance of success if you cover all the key domains. 

DBMS Interview Questions You Should Prepare For:

Here are a few DBMS interviews questions you should prepare for: 

Q. What is the difference between an RDBMS and DBMS?

A. The critical difference between the two is that DBMS offers an organized method for management, retrieval, and storage from a bulk of logically-related data. RDBMS also offers the same but additionally ensures relational integrity.

Q. State some of the benefits of DBMS.

A. DBMS provides several advantages as mentioned below:

- Data sharing: Several users can simultaneously use the data from a single database.

- Constraints of integrity: Integrity constraints ensure the data is stored in a refined way within the database.

- Redundancy control: DBMS supports mechanisms that integrate all the present data into one database to control data redundancy.

- Data independence: It enables the changing of data structures without the structure of any running programs getting affected.

- Recovery and backup facilities: It offers recovery and backup features that create automatic data backups and restore data whenever required. 

Q. What are the different languages in DBMS?

A. There are four fundamental languages in DBMS.

- Data Definition Language (DDL): This is made up of commands that help define the database. 

- Data Manipulation Language (DML): This is made up of commands that help manipulate the data within the database.

- Data Control Language (DCL): This is made up of commands that help with database system controls and permissions.

- Transaction Control Language (DCL): This is made up of commands that handle database transactions.

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Q. What does query optimization mean?

A. Query optimization refers to the phase when a plan is identified for query evaluation with the lowest cost estimation. Query optimization enters the fray when multiple methods and algorithms can be used to carry out the same job.

There are several advantages of query optimization.

- It provides output faster

- It can execute a higher volume of queries in lesser time

- It reduces the space and time complexity

Q. Are NULL values equal to zero or blank space?

A. No, NULL values and zero or blank space are not the same. A NULL value is one that is unknown, unassigned, not applicable, or unavailable. More fundamentally, zero is inherently a number, while a blank space is defined as a character.

Q. Can you explain atomicity and aggregation?

A. These are two fundamental definitions within the DBMS domain.

Atomicity: As a property, atomicity states that database modifications should follow either every rule or none at all. Thus, if any part of a transaction fails, the complete transaction fails.

Aggregation: This feature belongs to the E-R model. It allows relationship sets to participate in different relationship sets. 

Q. Explain the different levels of abstraction in DBMS.

A. DBMS has three levels of data abstraction. These are:

- Physical: The physical level is the lowest abstraction level. It describes how data gets stored.

- Logical: The logical level is higher than the physical level. It determines the type of data that gets stored within your database and the relationship between these data points.

- View: This is the highest abstraction level and describes only a specific part of a database. 

Q. Explain how an entity-relationship model works.

A. An entity-research model is a diagrammatic or visual approach to designing databases. In this model, real-world objects are represented as entities, and the relationships between them are mentioned. This model helps database administrators to easily understand the present schema.

Q. Explain these terms in the context of DBMS: Entity, Entity Type, and Entity Set.

A. These terms can be defined as follows:

- Entity: An entity is an object in the real world. Its attributes are merely that particular object’s characteristics. For instance, an employee could be an entity. The characteristics of this entity would be their name (empname), unique iD (empid), etc.

- Entity type: This is a collection or group of entities with the same attributes. Typically, entity types refer to one or several related tables within a specific database. This means entity type is a characteristic that identifies an entity uniquely. For instance, any employee’s empid or empname characteristics are always unique.

- Entity set: This is a collection of every entity of a particular type within a database. From the example above, a group of people, a handful of companies, or a team of employees will be grouped under a single entity set. 

Q. What is a relationship in the DBMS context? Mention the relationship types that exist. 

A. In DBMS, a relationship can be defined as a situation where two entities are related in some way or the other. In this situation, the table is made up of foreign key references to primary keys of other tables. 

Multiple relationship types exist in DBMS. In an instance where there are two Tables A and B, these relationships are:

- One-to-one relationships: This is when one row in Table A and one row in Table B are related.

- One-to-many relationships: This is when one row in Table A is related to several rows in Table B.

- Many-to-many relationships: This is when several rows in Table A could be related to several rows in Table B.

- Self-referencing relationships: This is when one record in Table A is related to Table A itself.

Also Read: To Have a Career in Data: 5 Best SQL Certifications to Have in 2022

Q. What are ACID properties in DBMS?

A. ACID is an acronym that means Atomicity, Consistency, Isolation, and Durability. The ACID helps ensure that data transactions get processed reliably in database systems. Here’s what each of the properties does:

- Atomicity: This refers to transactions that succeed or fail entirely. A transaction here refers to one logical operation of data. Even if a single part of any transaction fails, the entire transaction fails. The state of the database remains unchanged.

- Consistency: This ensures that data in the system meets all the rules of validation. In other words, no transaction can leave a database without finishing its state.

- Isolation: Isolation as a property aims to control concurrency.

- Durability: This means transactions will withstand anything. If you commit a transaction, it occurs no matter what.

Q. Name and describe the types of keys in a database.

A. There are primarily seven critical types in a database. These are:

  1. Candidate key: This refers to attributes that can identify a table uniquely. Any table can have multiple candidate keys. Besides this, one of the existing candidate keys in a table could become the Primary key.
  2. Super key: This refers to attributes that can identify a tuple uniquely. Thus, you can say a candidate key, primary key, and unique key can be a superkey, but the inverse isn’t true.
  3. Primary key: This refers to attribute sets that you can use to identify any tuple. For example, in an employee database, Employee ID and Registration Number could be candidate keys. Either of them can be taken as the primary key. 
  4. Unique key: This is akin to a primary key. However, a unique key allows NULL values within a column. In an employee database, the ‘years of experience’ field can become the unique key.
  5. Alternate key: An alternate key is a candidate key that isn’t chosen as the primary key. If Employee ID is taken as the primary key, Registration Number becomes the alternate key.
  6. Foreign Key: This key is an attribute that only takes values that are given as values of another feature concerning the attribute it refers to. 
  7. Composite Key: This key combines two columns or more which uniquely identify every tuple. 

These questions cover the key domains and areas that the interviewers may utilize to test you. For more holistic learning, talk to the experts at Koenig today. How you prepare for this interview will decide how your career path will unfold, so give it your best shot.

Anvesha Jain

Anvesha Jain has a great variety of knowledge in the education industry with more than 3 years of experience. He has also done work with many educational institutes as a Career counsellor. He also likes to write blogs on different topics like education and career guidance

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