MongoDB Aggregation Practice Challenges with Solutions (Part - 5)

🧩 MongoDB Practice Series – Aggregation Challenges with Solutions (Part 5)

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Welcome to Part 5 of the MongoDB Practice Series.

In this lesson, you will practice Aggregation in MongoDB.

Aggregation helps you perform calculations like:

• Total
• Average
• Count
• Grouping data

These skills are very useful for reports and analytics.

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🟢 Exercise 1: Count Total Documents

Problem:
Count the total number of students in the collection.

Solution:

db.students.countDocuments()

Learning Goal: Learn how to count records.

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🟡 Exercise 2: Calculate Average Value

Problem:
Find the average price of all products.

Solution:

db.products.aggregate([
  {
    $group: {
      _id: null,
      averagePrice: { $avg: "$price" }
    }
  }
])

Learning Goal: Use $group and $avg.

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🟡 Exercise 3: Calculate Total Sum

Problem:
Find the total revenue from all orders.

Solution:

db.orders.aggregate([
  {
    $group: {
      _id: null,
      totalRevenue: { $sum: "$totalAmount" }
    }
  }
])

Learning Goal: Use $sum to calculate totals.

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🔵 Exercise 4: Group Data by Category

Problem:
Count how many products exist in each category.

Solution:

db.products.aggregate([
  {
    $group: {
      _id: "$category",
      totalProducts: { $sum: 1 }
    }
  }
])

Learning Goal: Understand grouping by field value.

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🔵 Exercise 5: Find Maximum Value

Problem:
Find the highest product price.

Solution:

db.products.aggregate([
  {
    $group: {
      _id: null,
      highestPrice: { $max: "$price" }
    }
  }
])

Learning Goal: Use $max.

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🔴 Exercise 6: Group and Filter Results

Problem:
Find categories that have more than 5 products.

Solution:

db.products.aggregate([
  {
    $group: {
      _id: "$category",
      count: { $sum: 1 }
    }
  },
  {
    $match: {
      count: { $gt: 5 }
    }
  }
])

Learning Goal: Combine $group with $match.

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🚀 Mini Challenge

Create a collection called sales with fields:

• productName
• category
• quantity
• price

Then write queries to:

• Calculate total revenue (quantity × price)
• Find total sales per category
• Find the category with highest total sales

Try solving step by step.

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🎯 What’s Next?

In Part 6 of the MongoDB Practice Series, we will practice:

• Real-world schema design scenarios
• Embedding vs referencing decisions
• Designing scalable databases

Stay tuned for the next level!

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