🧪 MongoDB Practice Questions with Solutions (Beginner to Advanced)

Learning MongoDB is not just about reading concepts—it’s about practicing real problems.

Here, you’ll solve hands-on MongoDB exercises step by step. Each question includes:

✅ Problem
✅ Solution
✅ Explanation

By the end, you’ll feel confident working with real-world MongoDB scenarios.

🟢 Level 1: Beginner Exercises

✅ Q1: Create a Database and Collection

Problem:
Create a database called school and a collection called students.

Solution:

use school
db.createCollection("students")

Explanation:
use school creates (or switches to) the database and createCollection() creates a new collection.

---

✅ Q2: Insert Documents

Problem:
Insert 3 student records with fields: name, age, course.

Solution:

db.students.insertMany([
  { name: "Amit", age: 20, course: "BCA" },
  { name: "Sara", age: 22, course: "MCA" },
  { name: "John", age: 19, course: "BSc" }
])

Explanation:
insertMany() allows inserting multiple documents at once.

---

✅ Q3: Find All Documents

Problem:
Retrieve all students from the collection.

Solution:

db.students.find()

Explanation:
find() returns all documents in the collection.

---

✅ Q4: Filter Data

Problem:
Find students with age greater than 20.

Solution:

db.students.find({ age: { $gt: 20 } })

Explanation:
$gt means "greater than".

🟡 Level 2: Intermediate Exercises

✅ Q5: Update a Document

Problem:
Update "Amit"’s course to "B.Tech".

Solution:

db.students.updateOne(
  { name: "Amit" },
  { $set: { course: "B.Tech" } }
)

Explanation:
$set updates specific fields.

---

✅ Q6: Delete a Document

Problem:
Delete the student named "John".

Solution:

db.students.deleteOne({ name: "John" })

Explanation:
deleteOne() removes one matching document.

---

✅ Q7: Sort Data

Problem:
Sort students by age in descending order.

Solution:

db.students.find().sort({ age: -1 })

Explanation:
-1 = descending, 1 = ascending.

---

✅ Q8: Limit Results

Problem:
Show only 2 students.

Solution:

db.students.find().limit(2)

Explanation:
limit() restricts number of results.

🔵 Level 3: Advanced Exercises

✅ Q9: Design a Schema (Embedding vs Referencing)

Problem:
Design a schema for Users and Orders where each user can have many orders.

Solution:

// Users Collection
{
  _id: 1,
  name: "Amit"
}

// Orders Collection
{
  _id: 101,
  user_id: 1,
  product: "Laptop",
  price: 50000
}

Explanation:
Use referencing when data grows large. Avoid embedding too many orders inside a single document.

---

✅ Q10: Aggregation Query

Problem:
Find the average age of students.

Solution:

db.students.aggregate([
  {
    $group: {
      _id: null,
      averageAge: { $avg: "$age" }
    }
  }
])

Explanation:
$group is used for aggregation and $avg calculates average.

---

✅ Q11: Find Duplicate Data

Problem:
Find duplicate student names.

Solution:

db.students.aggregate([
  {
    $group: {
      _id: "$name",
      count: { $sum: 1 }
    }
  },
  {
    $match: {
      count: { $gt: 1 }
    }
  }
])

Explanation:
Groups data by name and filters duplicates using $match.

🚀 Bonus Challenge

Challenge:
Design a database for a blog system with Users, Posts, and Comments.

Which data will you embed?
Which data will you reference?
Why?

🎯 Final Thoughts

If you completed these exercises, you now understand:

CRUD operations (Create, Read, Update & Delete)
Filtering & sorting
Aggregation
Schema design basics

The best way to learn MongoDB is:
Practice → Build → Break → Fix → Repeat

📚 What to Learn Next

MongoDB with Python (PyMongo)
Indexing for performance
Real-world projects

💬 Your Turn:
Which question did you find most challenging? Let us know in the comments!

← MongoDB Tutorial Part 2 →

🧪 Practice Task – CRUD Basics in SQL & MongoDB

Here's a Practice Task + Mini Assignment that complements Part 6: CRUD Operations in SQL vs NoSQL. It's designed to reinforce the differences in syntax and logic between SQL and MongoDB, while staying simple and highly practical for beginners.

🎯 Objective:

Perform basic Create, Read, Update, and Delete operations in both SQL and NoSQL (MongoDB).

🔹 Scenario: School Students Data

You are managing a student database and need to do the following:

Add a new student
Fetch the student's data
Update the student’s class
Delete the student’s record

📌 A. SQL Practice

1. Create

INSERT INTO Students (StudentID, Name, Class)
VALUES (2, 'Ravi Kumar', '10B');

2. Read

SELECT * FROM Students WHERE StudentID = 2;

3. Update

UPDATE Students SET Class = '10C' WHERE StudentID = 2;

4. Delete

DELETE FROM Students WHERE StudentID = 2;

📌 B. MongoDB Practice

1. Create

db.students.insertOne({
  student_id: 2,
  name: "Ravi Kumar",
  class: "10B",
  marks: [{ subject: "English", score: 82 }]
});

2. Read

db.students.findOne({ student_id: 2 });

3. Update

db.students.updateOne(
  { student_id: 2 },
  { $set: { class: "10C" } }
);

4. Delete

db.students.deleteOne({ student_id: 2 });

📝 Mini Assignment: Build Your Own CRUD Set

🔹 Instructions:

Choose a student name and add them to both SQL and NoSQL.
Add a subject and score for them (embedded in NoSQL).
Read and display their data.
Change their class and update their English score to 90.
Finally, delete the record in both systems.

💡 Challenge (Optional):

In SQL, insert marks into a separate Marks table and join it to fetch the student’s full profile.
In MongoDB, use $push to add a new subject to the marks array.

✅ Bonus: MongoDB `$push` Example

db.students.updateOne(
  { student_id: 2 },
  { $push: { marks: { subject: "Science", score: 88 } } }
);

Do you Know: The $push operator is used to add a new element to an array field in MongoDB.

Tell Us in Comments:

Which syntax do you find easier — SQL or MongoDB? Share your thoughts in the comments!

Also, Try the assignment above and share your solution in the comments.

To know about CRUD opreations read Part 6: CRUD Operations in SQL vs NoSQL – A Beginner's Guide

✅ What’s Next?

Next: solution for the mini assignment in both SQL and NoSQL

← previous Next →

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