MongoDB Database Developer Interview Questions and Answers

Round duration - 60 minutes
Round difficulty - Easy

This was a technical round with questions on DBMS.

Q1. What is data integrity?
Ans. 
Data integrity refers to the accuracy, consistency, and reliability of data throughout its lifecycle.
• Data integrity ensures that data is accurate and consistent in storage and transmission.

• It involves maintaining the quality and reliability of data over time.

• Methods for ensuring data integrity include checksums, encryption, and error detection codes.

• Examples of data integrity violations include data corruption, unautho
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Q2. What is a trigger in the context of a database management system?
Ans. 
A trigger is a special type of stored procedure that automatically executes when certain events occur in a database.
• Triggers are used to enforce business rules, maintain data integrity, and automate repetitive tasks.

• They can be triggered by INSERT, UPDATE, or DELETE operations on a table.

• Examples of triggers include auditing changes to a table, updating related tables when a record is modified, or enforcing referential
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Q3. What is the difference between clustered and non-clustered indexes in a database management system?
Ans. 
Clustered indexes physically order the data in the table, while non-clustered indexes do not.
• Clustered indexes determine the physical order of data in the table, while non-clustered indexes do not.

• A table can have only one clustered index, but multiple non-clustered indexes.

• Clustered indexes are faster for retrieval of data, especially range queries, compared to non-clustered indexes.

• Non-clustered indexes are stored se...read more
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Round duration - 60 minutes
Round difficulty - Easy

Technical interview round with questions on DBMS.

Q1. What is the difference between UNION and UNION ALL in SQL?
Ans. 
UNION combines and removes duplicates, UNION ALL combines without removing duplicates.
• UNION merges the result sets of two or more SELECT statements and removes duplicates.

• UNION ALL merges the result sets of two or more SELECT statements without removing duplicates.

• UNION is slower than UNION ALL as it involves removing duplicates.

• Example: SELECT column1 FROM table1 UNION SELECT column1 FROM table2;

• Example: SELECT column...read more
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Q2. What are the functions of a cursor in PL/SQL?
Ans. 
A cursor in PL/SQL is used to retrieve and process multiple rows of data one at a time.
• Allows iteration over a result set

• Retrieves data row by row

• Can be used to update or delete rows in a table

• Must be declared, opened, fetched, and closed
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Q3. Write a SQL query to fetch the nth highest salary from a table.
Ans. 
SQL query to fetch the nth highest salary from a table
• Use the ORDER BY clause to sort salaries in descending order

• Use the LIMIT clause to fetch the nth highest salary
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Round duration - 30 minutes
Round difficulty - Easy

This was a managerial round with typical behavioral problems.

Round duration - 60 minutes
Round difficulty - Medium

The interviewer was really cool. He realized that I mostly work on java applications so he chose to ask me stuff related to that. He didn't want me to know the answer well but just wanted me to approach to it, maybe think more. He went through my resume back and forth and asked mostly about all my projects and their logic and how could I take them to the next level.
Tips: Be confident. Its okay not to know any answer, just try giving it a shot in the approach.

Q1. What is the difference between an abstract class and an interface in Java?
Ans. 
Abstract class can have both abstract and non-abstract methods, while interface can only have abstract methods.
• Abstract class can have constructors, member variables, and methods with implementation.

• Interface can only have abstract methods and constants.

• A class can implement multiple interfaces but can only extend one abstract class.

• Example: Abstract class - Animal with abstract method 'eat', Interface - Flyable with m
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Q2. What is the difference between 'final', 'finally', and 'finalize' in Java?
Ans. 
final is a keyword used to declare constants, finally is a block used in exception handling, and finalize is a method used for cleanup.
• final is a keyword used to declare constants in Java, meaning the value cannot be changed once assigned. Example: final int x = 10;

• finally is a block used in exception handling to ensure a piece of code is always executed, whether an exception is thrown or not. Example: try { // code } ...read more
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Q3. What is the difference between the private and final access modifiers in Java?
Ans. 
Private restricts access to the class itself, while final prevents inheritance and method overriding.
• Private access modifier restricts access to the class itself, while final access modifier prevents inheritance and method overriding.

• Private members are only accessible within the same class, while final classes cannot be extended and final methods cannot be overridden.

• Example: private int num; - num can only be accesse...read more
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Q4. What are the steps for establishing a JDBC connection?
Ans. 
Establishing a JDBC connection involves loading the driver, creating a connection, creating a statement, executing queries, and handling exceptions.
• Load the JDBC driver using Class.forName() method

• Create a connection using DriverManager.getConnection() method

• Create a statement using connection.createStatement() method

• Execute queries using statement.executeQuery() method

• Handle exceptions using try-catch blocks
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Q5. What is JSON?
Ans. 
JSON is a lightweight data interchange format used to store and transmit data between a server and a web application.
• JSON stands for JavaScript Object Notation.

• It is easy for humans to read and write, and easy for machines to parse and generate.

• JSON is language-independent and can be used with any programming language.

• Example: {"name": "John", "age": 30}

• Example: [{"name": "Alice", "age": 25}, {"name": "Bob", "age": 35}
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Q6. What do you know about garbage collection in Java?
Ans. 
Garbage collection in Java is the process of automatically managing memory by deallocating objects that are no longer needed.
• Garbage collection helps in preventing memory leaks by reclaiming memory used by objects that are no longer referenced.

• Java uses a garbage collector to automatically manage memory, unlike languages like C++ where memory management is manual.

• Garbage collection in Java can be triggered by calling S...read more
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Round duration - 30 minutes
Round difficulty - Easy

I wouldn't say it went great but it was fine. I did not think I would clear it as for most of the questions the interviewer seemed disappointed and wanted more out of me.