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ERD (Entity Relationship Diagram) Interview Questions — For Database Design & Modeling Roles (2025 Edition)

 
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 SQL Admin
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If you’re preparing for database design or data modeling interviews in 2025, you’ll definitely face ERD-related questions.

ERD (Entity Relationship Diagram) questions test your ability to design efficient database schemas, define relationships, and convert real-world business processes into structured database models.

These real-time scenario-based ERD questions are frequently asked in Infosys, Accenture, Capgemini, and Deloitte interviews — ideal for data analysts, BI developers, and DB designers.

🔹 Top ERD (Entity Relationship Diagram) Interview Questions (2025 Edition)

1️⃣ What is an ERD and why is it important?

Answer:
An Entity Relationship Diagram (ERD) is a visual representation of entities, their attributes, and the relationships between them.
It’s used to design the logical structure of a database before actual implementation.
✅ Helps ensure data integrity, reduce redundancy, and improve scalability.

2️⃣ What are the main components of an ERD?

  • Entity: A real-world object (e.g., Customer, Order).

  • Attribute: Property of an entity (e.g., Name, ID, Price).

  • Relationship: Association between entities (e.g., Customer → places → Order).

  • Primary Key (PK): Unique identifier of each entity.

  • Foreign Key (FK): References PK from another table to form a relationship.

3️⃣ Explain the different types of relationships in ERD.

Relationship TypeExampleDescription
One-to-One (1:1)Person → PassportEach person has one passport.
One-to-Many (1:N)Customer → OrdersOne customer can place many orders.
Many-to-Many (M:N)Students ↔ CoursesStudents can enroll in many courses, and courses can have many students.

📌 Many-to-many relationships are usually implemented through a junction (bridge) table.

4️⃣ How do you convert an ERD into database tables?

  1. Each entity becomes a table.

  2. Each attribute becomes a column.

  3. Primary keys and foreign keys are added to define relationships.

Example:
Entities:

  • Customer (Customer_ID, Name, Email)

  • Order (Order_ID, Order_Date, Customer_ID)

Relationship → One-to-Many

 
CREATE TABLE Customer (
Customer_ID NUMBER PRIMARY KEY,
Name VARCHAR2(100),
Email VARCHAR2(100)
);

CREATE TABLE Orders (
Order_ID NUMBER PRIMARY KEY,
Order_Date DATE,
Customer_ID NUMBER REFERENCES Customer(Customer_ID)
);

5️⃣ What is the difference between logical and physical data models?

TypeDescriptionExample
Logical ModelFocuses on what data is required and how entities are relatedERD
Physical ModelDescribes how data will be stored (tables, indexes, constraints)Actual database schema

✅ Accenture often tests this difference to check data modeling clarity.

6️⃣ What are normalization and denormalization?

  • Normalization:
    Process of organizing data to reduce redundancy.
    Common forms:

    • 1NF: Atomic columns

    • 2NF: Remove partial dependency

    • 3NF: Remove transitive dependency

  • Denormalization:
    Combining tables to improve query performance (used in reporting and data warehousing).

📌 Infosys interviewers often ask: “Why would you denormalize a data model?”

7️⃣ How do you represent optional and mandatory relationships in ERD?

  • Mandatory Relationship: Shown with a solid line — e.g., Each Order must have a Customer.

  • Optional Relationship: Shown with a dashed line — e.g., Each Customer may have a Discount record.

8️⃣ What is cardinality in ERD?

Cardinality defines the number of instances one entity can have in relation to another.
Example:

  • A customer can place many orders → (1:N).

  • An order belongs to one customer → (N:1).

✅ Cardinality determines foreign key placement in your database.

9️⃣ Real-Time Scenario: Design an ERD for an Online Learning Platform

Entities:

  • Student, Course, Instructor, Enrollment
    Relationships:

  • Student ↔ Enrollment (1:N)

  • Course ↔ Enrollment (1:N)

  • Instructor ↔ Course (1:N)

Junction Table: Enrollment(Student_ID, Course_ID, Enroll_Date)

✅ Common real-world scenario asked in Deloitte & Capgemini interviews.

💡 Pro Tip:

During interviews, when asked to “draw an ERD,” explain your approach before design:

“I start by identifying entities from the business use case, then define relationships, keys, and finally convert them into normalized database tables.”

This structured explanation shows professional thinking — and earns extra points.

🧩 Conclusion

These ERD (Entity Relationship Diagram) interview questions (2025 Edition) help you master database design fundamentals, relationships, and real-world modeling scenarios.

Companies like Infosys, Accenture, and Capgemini assess how well you can translate a business process into a clear, scalable data model — not just how you draw diagrams.

Keep practicing with sample case studies (e.g., Hospital Management, Banking System, E-commerce) to strengthen your ERD and normalization skills.


Topic Tags
ERD Interview Questions 2 Database Design Intervie Data Modeling Real-Time Entity Relationship Diag Normalization and Relati

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