DBMS Interview Questions You MUST Know

dbms interview questionsDatabase Management Systems (DBMS) form the backbone of large modern-world company and enterprises. Most of the employee related and business related data is stored and accessed through DBMS software.  However, because of the complexity of many of these DBMS software offerings, most companies need to hire technical experts solely for the purpose of administering these databases – which is good new for you, of course, if you are a technical student! This beginners course on Oracle Database administration is a great place to start. There is always a demand for data analysts and database administrators in the marketplace, specializing in different DBMS software products like Oracle and MYSQL. You can make a good career for yourself in the field.

Cracking an interview may seem daunting, but you just need to prepare right. It’s all about keeping calm and showing you know what the interviewer is talking about. This course case help you master the interview mindset and strategies.

In this article, we’re going to give you a list of the most common DBMS interview questions asked to you if you are a recent graduate.  At any point of time, you can look up the details about these concepts in our advanced database course.

What is a Database?

(Don’t think the interviewer won’t ask you basic questions! They want to make sure you’ve got your basic concepts right!) A database is a collection of data that has been organized for easy access and retrieval. A database can be both a paper-based and a computer-based database. If it’s an electronic database, it is designed in such a way that a computer can easily access it and retrieve required pieces of data.

What is a Database Management System? What are the Different Types?

A database management software system (DBMS) lets you store, make changes to and retrieve data from an electronic database. There are different types of databases, organized on the basis of how they are managed. Hierarchical DBMS are those that store data in such a way as to make a piece of data always a subordinate of another piece of data (like the hierarchy found in the army). Network DBMS are those in which the data members of the database are connected in a network, in a one to one relationship. Relational DBMS (RDBMS) are the most popular form of database software. Data members of a RDB are stored in a form of a table, and the members of the table have unique attributes. Object-oriented databases are unique in that they can store pieces of media (video, audio and photos). They objects (containing data and the methods that let you handle the data) to make up the database. (You can learn more about database design in this course).

What is SQL?

SQL is the language that lets you work with databases. Commands in SQL let you modify, store and retrieve items from a database. The language has been standardized by the ANSI (American National Standards Institute) – which means that it can be used with a wide variety of DBMS software products from around the world.

(If you’re new to SQL, you should first learn the basics. This beginners course in SQL database is a good place to start. Learning SQL is easy. The language is self-descriptive and the commands are easy to remember. It can also help you do almost everything you could want from a database. )

How Do You Combine Rows in SQL?

(Now that the interviewer has checked your fundamentals, they’ll move into the real technical stuff) JOIN in SQL lets you combine rows from the tables in your database, so that you don’t have to retype all the data by yourself. The command works only if there is a common field between the two (or more) tables that you are trying to combine. If there is no common field between the two, you will get a NULL result.

How Would You Combine a Table Using Join? Show Us an Example.

The most commonly used type of JOIN is the INNER JOIN. The syntax of INNER JOIN is as follows:

Select column1, column2, column3…
FROM table 1
INNER JOIN table 2
ON table 1.column1 = table2.column2;

Let’s say we have two tables called “Students” and “Teachers”. The “Students” table contains the following information:

TeacherID
StudentID
DateofJoining
2
101
12th March
3
102
18th June
5
103
20th Dec

 

The “Teachers” table contains the following information:

TeacherID
NameofTeacher
Subject
1
Anna
Biology
2
Marie
Math
10
Jo
Business Studies

These tables have a common field between them: the “Teacher ID” column. It’s okay if not all the members of the tables match, but there must be a definite relationship between the two for the INNER JOIN command to work.

SELECT Students.StudentID, Teachers.NameofTeacher, Teachers.Subject
 FROM Students
 INNER JOIN Teachers
 ON Students.TeacherID=Teachers.TeacherID;

The result of this will be as follows:

StudentID
NameofTeacher
Subject
101
Marie
Math
102
Jessica
Physics
103
Chloe
Chemistry
110
Ana
Biology
112
Jo
Business Studies

The other types of SQL JOINS (which you probably won’t be asked about, but should still study) are RIGHT JOIN, FULL JOIN and LEFT JOIN.

What is a View in SQL? How Do You Create a View in SQL?

A view is a virtual table that is not really present in your database – you just obtain it in response to your query. The syntax to create a View table is as follows:

CREATE VIEW name_of_view AS
SELECT name_of_view
FROM name_of_table
WHERE specify_condition

A view will just be like any other regular table. It will contain rows and columns and the data it will show will depend on your query.

For example, if you wanted to view a list of all “NewMovies” from your database containing movies, called “Movies” you could use the following View query:

CREATE VIEW [Recent Movies] AS
 SELECT MovieID, MovieName
FROM Movies
WHERE NewMovies = yes

This will only return movies marked new from your database.

(Note: if of these programs seem unfamiliar to you, you should head over to this course to quickly master SQL)

What are Keys in DBMS?

This is one question you’ve probably encountered before in your exams before. Keys let you define relationships between the tables in your database. They also ensure that every record in your table has a unique identity, and can be retrieved with the help of querying one or more fields in your database.

What are the Different Types of Keys?

There are four types of keys you encounter most often when using a DBMS: super key, candidate key, primary key and foreign key. A super key is the key taken as a set of attributes that can uniquely identify each record of the table in your database. The candidate key is the subset of your super key. It is taken as the collection of fields from which you get your primary key. Candidate keys help you isolate the attributes that your primary key should be defined by. A primary key is selected from candidate keys. It is the key that is most suitable of becoming the most important key in the table. As a subset of the super key, it helps you identify each record in your table. The other two keys you should know about include composite key and foreign key.

These are just some of the most common questions you will likely encounter during your interview. The best way to prepare for an interview is to master your subject. Put in the time and effort to make sure you’re comfortable with DBMS systems. And of course, along with the technical aspects, you need to make sure you have the right attitude and approach. Do check out this course to career mind mastery for the blueprint to interview success.