DBMS Interview Questions & Answers

1. Basic DBMS Interview Questions

1. What is DBMS?
   A DBMS (Database Management System) is software that allows users to store, retrieve, manage, and manipulate data efficiently.
2. What are the advantages of DBMS?
   ✔ Reduced data redundancy ✔ Improved data consistency ✔ Data security ✔ Backup and recovery ✔ Multi-user access
3. What is a database?
   A database is an organized collection of related data stored electronically for easy access and management.

2. DBMS Architecture & Models

1. What are the different database models?
   ✔ Hierarchical Model ✔ Network Model ✔ Relational Model ✔ Object-Oriented Model
2. What is the Relational Model?
   It organizes data into tables (relations) consisting of rows and columns, and uses keys to maintain relationships.
3. What is schema?
   A schema defines the logical structure of a database, including tables, fields, and relationships.

3. Keys in DBMS

1. What is a primary key?
   A primary key uniquely identifies each record in a table and cannot contain NULL values.
2. Difference between primary key and foreign key?
   Primary Key → Identifies records uniquely in the same table Foreign Key → Links records between two tables
3. What is a composite key?
   A key formed using two or more columns to uniquely identify a record.

4. SQL Interview Questions

1. What is SQL?
   SQL (Structured Query Language) is used to communicate with relational databases.
2. Difference between DELETE and TRUNCATE?
   DELETE → Removes selected rows, can be rolled back TRUNCATE → Removes all rows, cannot be rolled back
3. What is JOIN?
   JOIN is used to combine records from multiple tables based on related columns.

5. Aggregate & Grouping

1. What is GROUP BY?
   GROUP BY groups rows with same values and applies aggregate functions on them.
2. Difference between WHERE and HAVING?
   WHERE → Filters rows HAVING → Filters grouped results
3. Name some aggregate functions.
   COUNT(), SUM(), AVG(), MIN(), MAX()

6. Advanced DBMS Questions

1. What is a subquery?
   A subquery is a query written inside another SQL query.
2. What is a data warehouse?
   A centralized repository that stores historical data for analysis and decision making.
3. Difference between OLTP and OLAP?
   OLTP → Transaction processing OLAP → Analytical processing

7. Conceptual / HR-Friendly Questions

1. Why do you want to work with databases?
2. How does DBMS help in real-world applications?
3. Explain DBMS using a real-life example.

Practice Task