10 Essential Database Management System Questions

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10 Key Database Management System Interview Questions

Q1. List various language types that are available in the Database Management System (DBMS).

1. DML: This is short for Data Manipulation Language, which helps in few manipulations in the database like deletion, insertion, etc. (utilizing some set of SQL queries like DELETE, INSERT, SELECT, and UPDATE)
2. DDL: It stands for Data Definition Language, which is leveraged to define the database and schema structure by utilizing SQL queries like ALTER, CREATE, DROP, RENAME, and DROP. 
3. DCL: Data Control Language can control the users’ access inside the database by utilizing few SQL queries like REVOKE and GRANT. 

Q2. Why is there normalization in DBMS?

A: In DBMS, it is the process of analyzing the relational schemas that are based on their respective functional dependencies and the primary keys to satisfy specific properties, like:

• Minimizing the Delete, Insert, and Update Anomalies.
• Minimizing the data’s redundancy.

Q3. Elaborate on the primary difference between UNION and UNION ALL?

A: Both of them are used to join the data from 2 or more tables. The main difference is that UNION ALL does not remove the duplicate rows. It just picks all the data from the tables. 

On the other hand, UNION removes duplicate rows and selects the distinct rows after combining the data from the tables. 

Q4. Elaborate on the integrity rules of Database Management Systems.

A: So we have two crucial integrity rules of DBMS, that are:

1. Referential Integrity: This rule implies that the value of a Foreign Key is a NULL value or is supposed to be the primary key of any other relation. 
2. Entity Integrity: The rule is that the value of a Primary Key can never possess a NULL value. 

Q5. Say something about functional dependency in Database Management Systems.

A: For example, suppose you have a relation ‘R1’ having two attributes as Y and Z. In that case, the functional dependency among these two attributes can be represented as Y->Z, which implies that Z is functionally reliant on Y. 

Q6. List various types of SQL joins.

A: There are four types of joins in SQL:

1. Full Join: This join returns the rows from all the tables on which the join condition has been put, and the rows which don’t match hold null values. 
2. Inner Join: This join can collect the data among the tables that are common in both tables.
3. Left Join: This join type tends to return all the rows from the table on the left side of the join. Additionally, it returns only those matching rows from the right side of the join. 
4. Right, Join: This join type is the opposite of the above-mentioned left join. And it only returns the matching rows from the left side of the join. 

Q7. Explain 1NF in the Database Management System.

A: 1NF stands for First Normal Form. 

Moreover, this is the most accessible form of the normalization process, which articulates that the domain of an attribute should have only atomic values. Its purpose is to remove the duplicate columns from the table. 

Q8. Explain 2NF in the Database Management System.

A: 2NF stands for Second Normal Form.

For a table to have 2NF, it needs to satisfy these criteria:

• Every non-prime attribute of a table is meant to be functionally dependent in totality on the primary key. 

Q9. Explain 3NF in DBMS.

A: 3NF stands for Third Normal Form. 

If a table needs to be in 3NF, it eventually requires these criteria:

• Every non-prime attribute of that table is meant to be non-transitively dependent on each key of the table.
• The table is in the Second Normal Form, i.e., 2NF.

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Q10. Explain BCNF in DBMS.

A: Stricter than 3NF, BCNF is short for Boyce Codd Normal Form.

We can conclude that a table is in BCNF if it complies with these criteria:

• For every functional dependency X->Y that is there, X is the super key.

Q11. Comment something on Entity, Entity Set, and Entity Type in the Database Management System?

A: 

• Entity: A thing, place, or object that has its independent existence in the actual world and whose data you can store in a database. Some common examples are a book or a person. 
• Set: A compilation of entities of the same type. An example of an entity set could be a collection of bottles manufactured in a factory. 
• Type: It is a compilation of entities having the exact attributes. 

An example could be the STUDENT table, which carries rows, and each row is an entity that holds attributes like age, ID, and students’ names. Therefore, STUDENT is an entity type having entities of the same qualities. 

Q12. Say something about the concept of sub-query in terms of SQL.

A: It is a query mentioned inside another question and is also known as an inner query (found inside the outer query). 

Q13. In short, explain the use of SQL.

A: SQL is a short form for Structured Query Language. Its purpose is to interact with the relational databases in the form of updating/modification and insertion of the data in the database. 

Ending Notes

So here comes the end. I’m sure that now you’re aware of some database management questions that could be useful for your future interviews. 

Also, this goes without saying. Don’t forget to practice all crucial and practical DBMS topics to understand better.

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