Almost every computer science-related job requires knowledge about databases. Here are 10 commonly asked database management system interview questions.
1. What is a DBMS?
DBMS stands for “database management system”. A DBMS is a software that allows the storage, access, retrieval, and manipulation of data while maintaining security. It implements ACID (atomicity, durability, isolation, consistency) properties to ensure efficient transaction and data management without any kind of data corruption.
2. What is a database?
As per Oracle’s website, “A database is an organized collection of structured information, or data, typically stored electronically in a computer system. A database is usually controlled by a database management system (DBMS).“
Without a database, it becomes difficult to handle data, especially one comprising several relations.
3. What are some advantages of using a database management system (DBMS)?
Some key benefits of using a DBMS are:
- Redundancy management: DBMS provides the mechanism for controlling redundancy of data inside the databases by integrating the same into one specific single database. As data gets stored in one single database, the chance of duplicity is removed.
- Sharing of Data: A DBMS makes it possible to share the data with multiple users who belong to different roles. The database administrator decides how the same database is accessible to multiple users.
- The facility of backup and recovery of data.
- Maintenance of integrity constraint.
- Maintenance of data independence.
4. What is the need for normalization in a DBMS?
DBMS Interview Questions are incomplete without a question on normalization. Normalization is required for the following reasons:
- To minimize data redundancy. This in turn reduces inconsistencies that may occur due to repeated information.
- Helps to filter dependencies.
- Takes care of anomalies that may occur during insert, delete, and update operations.
5. What are the different languages used in a DBMS?
A database management system (DBMS) uses the following languages:
- DDL: DDL stands for data definition language. It is used to give a proper definition of the database and maintains the schema structure through CREATE, TRUNCATE, ALTER, RENAME, and DROP commands.
- DCL: DCL stands for data control language. It is used for controlling the access that users have within the database. Some of the key DCL commands are REVOKE and GRANT.
- DML: DML stands for data manipulation language. It is used for manipulating the data within the database. SELECT, DELETE, INSERT, and UPDATE are DML commands.
6. What is the need for SQL in DBMS?
SQL stands for “structured query language”. SQL is used for interacting with relational databases through insertion, deletion, and modification of data in the database. It can also be used for building complex queries to retrieve data from the database.
7. What are the primary key and foreign key in a database?
A primary key uniquely identifies a record in the table, whereas a foreign key is a field in the table that is the primary key in another table. There can be only one primary key in a table while consisting of multiple foreign keys. A primary key field cannot accept NULL values, whereas a foreign key field accepts NULL values.
Read More about Database Management System on Wikipedia
8. What is the difference between the primary key and the unique key in a database?
Some of the key differences between a primary key and a unique key are:
- A primary key does not accept NULL values. A unique key accepts NULL values.
- A table can have only one primary key but multiple unique keys.
9. What is a subquery?
Advanced level database interview questions often include the writing of subqueries. A subquery is a query written inside some other query. Hence, it is a “nested” query. The outer query uses the result generated by the subquery. A subquery is also known as an inner query.
10. What is the difference between DROP, DELETE, and TRUNCATE commands?
DROP, DELETE, and TRUNCATE are frequently used SQL queries.
DROP: Removes the table’s structure and its contents.
DELETE: Removes specific contents from the table (based on a condition) but not its structure.
Truncate: Removes the entire content of the table along with its structure.
Do you know about concepts or topics necessary for database interview preparation? What are the most difficult database management system interview questions you have faced? We’d love to know more in the comments.