$gt and $gte for greater than in MongoDB - Mini Project: Build & Apply

$gt and $gte for greater than in MongoDB

📖 Scenario: You are managing a small online bookstore database. You want to find books with prices greater than certain amounts to offer special discounts.

🎯 Goal: Build MongoDB queries using $gt and $gte operators to filter books by price.

📋 What You'll Learn

Create a collection named books with specific book documents

Add a variable to hold a price threshold

Write a query using $gt to find books priced greater than the threshold

Write a query using $gte to find books priced greater than or equal to the threshold

💡 Why This Matters

🌍 Real World

Filtering products or items in a database by price or other numeric values is common in e-commerce and inventory management.

💼 Career

Understanding MongoDB query operators like $gt and $gte is essential for backend developers and data analysts working with NoSQL databases.

1

DATA SETUP: Create the books collection with 4 books

Create a MongoDB collection called books with these exact documents: { title: "Book A", price: 15 }, { title: "Book B", price: 20 }, { title: "Book C", price: 25 }, { title: "Book D", price: 30 }

MongoDB

// Insert the 4 book documents into the books collection
// Your code here

Hint

Use db.books.insertMany([...]) with the exact book documents.

2

CONFIGURATION: Set a price threshold variable

Create a variable called priceThreshold and set it to 20

MongoDB

db.books.insertMany([
  { title: "Book A", price: 15 },
  { title: "Book B", price: 20 },
  { title: "Book C", price: 25 },
  { title: "Book D", price: 30 }
])

// Create priceThreshold variable
// Your code here

Hint

Use const priceThreshold = 20 to set the threshold.

3

CORE LOGIC: Query books with price greater than priceThreshold using $gt

Write a MongoDB query called booksGreaterThan that finds all books where price is greater than priceThreshold using the $gt operator

MongoDB

db.books.insertMany([
  { title: "Book A", price: 15 },
  { title: "Book B", price: 20 },
  { title: "Book C", price: 25 },
  { title: "Book D", price: 30 }
])

const priceThreshold = 20

// Create booksGreaterThan query using $gt
// Your code here

Hint

Use db.books.find({ price: { $gt: priceThreshold } }) to find books priced greater than the threshold.

4

COMPLETION: Query books with price greater than or equal to priceThreshold using $gte

Write a MongoDB query called booksGreaterOrEqual that finds all books where price is greater than or equal to priceThreshold using the $gte operator

MongoDB

db.books.insertMany([
  { title: "Book A", price: 15 },
  { title: "Book B", price: 20 },
  { title: "Book C", price: 25 },
  { title: "Book D", price: 30 }
])

const priceThreshold = 20

const booksGreaterThan = db.books.find({ price: { $gt: priceThreshold } })

// Create booksGreaterOrEqual query using $gte
// Your code here

Hint

Use db.books.find({ price: { $gte: priceThreshold } }) to find books priced greater than or equal to the threshold.

Practice

1. What does the $gt operator do in a MongoDB query?

easy

A. Finds documents where the field value is less than the specified value.

B. Finds documents where the field value is equal to the specified value.

C. Finds documents where the field value is strictly greater than the specified value.

D. Finds documents where the field value is greater than or equal to the specified value.

Solution

1. Step 1: Understand the meaning of $gt

   The $gt operator means "greater than" and selects values strictly larger than the given number.

2. Step 2: Compare with other operators

   $gte means "greater than or equal to", so it includes the number itself, unlike $gt.

3. Final Answer:

   Finds documents where the field value is strictly greater than the specified value. -> Option C

4. Quick Check:

   $gt = strictly greater than [OK]

Hint: Remember: $gt means strictly greater than [OK]

Common Mistakes:

• Confusing $gt with $gte
• Thinking $gt includes equal values
• Mixing $gt with less than operators

2. Which of the following is the correct syntax to find documents where the field age is greater than or equal to 18 in MongoDB?

easy

A. { age: { $gte: 18 } }

B. { age: { $gt: 18 } }

C. { age: { $gte: "18" } }

D. { age: { $gte: > 18 } }

Solution

1. Step 1: Check the operator and syntax

   The correct operator for "greater than or equal to" is $gte, and it must be used as { field: { $gte: value } }.

2. Step 2: Validate the value type and format

   The value should be a number (18), not a string or invalid syntax like > 18.

3. Final Answer:

   { age: { $gte: 18 } } -> Option A

4. Quick Check:

   Correct syntax uses $gte with number [OK]

Hint: Use { field: { $gte: number } } for greater or equal [OK]

Common Mistakes:

• Using quotes around numbers
• Writing invalid syntax like $gte: > 18
• Confusing $gt and $gte

3. Given the collection products with documents:

{ "name": "Pen", "price": 5 }

{ "name": "Notebook", "price": 10 }

{ "name": "Backpack", "price": 20 }

What will be the result of the query db.products.find({ price: { $gt: 10 } })?

medium

A. [{ "name": "Notebook", "price": 10 }, { "name": "Backpack", "price": 20 }]

B. [{ "name": "Pen", "price": 5 }]

C. []

D. [{ "name": "Backpack", "price": 20 }]

Solution

1. Step 1: Understand the query condition

   The query uses $gt: 10, so it selects documents where price is strictly greater than 10.

2. Step 2: Check each document's price

   "Pen" has price 5 (not > 10), "Notebook" has price 10 (not > 10), "Backpack" has price 20 (greater than 10).

3. Final Answer:

   [{ "name": "Backpack", "price": 20 }] -> Option D

4. Quick Check:

   Only price > 10 matches [OK]

Hint: Remember $gt excludes equal values [OK]

Common Mistakes:

• Including documents with price equal to 10
• Confusing $gt with $gte
• Selecting documents with price less than 10

4. You wrote the query db.users.find({ age: { $gte: 21 } }) but it returns no results even though some users are 21 or older. What is the likely problem?

medium

A. You should use $gt instead of $gte.

B. The field name age is misspelled in the documents.

C. The query syntax is incorrect; $gte cannot be used here.

D. MongoDB does not support $gte operator.

Solution

1. Step 1: Check the query syntax

   The syntax { age: { $gte: 21 } } is correct and supported by MongoDB.

2. Step 2: Consider data issues

   If no results appear, likely the field age is misspelled or missing in documents, so no matches occur.

3. Final Answer:

   The field name age is misspelled in the documents. -> Option B

4. Quick Check:

   Field name mismatch causes no results [OK]

Hint: Check field names carefully if no results [OK]

Common Mistakes:

• Assuming $gte is unsupported
• Switching $gte to $gt unnecessarily
• Ignoring possible typos in field names

5. You want to find all orders with a total amount greater than or equal to 100 but less than 200. Which MongoDB query correctly uses $gte and $gt to achieve this?

hard

A. { total: { $gte: 100, $lt: 200 } }

B. { total: { $gt: 100, $gte: 200 } }

C. { total: { $gte: 100, $gt: 200 } }

D. { total: { $gte: 100, $gt: 199 } }

Solution

1. Step 1: Understand the range conditions

   You want totals >= 100 and < 200, so use $gte: 100 and $lt: 200 (less than 200).

2. Step 2: Check each option's operators

   { total: { $gte: 100, $lt: 200 } } correctly uses $gte: 100 and $lt: 200. Other options misuse operators or values.

3. Final Answer:

   { total: { $gte: 100, $lt: 200 } } -> Option A

4. Quick Check:

   Use $gte for lower bound, $lt for upper bound [OK]

Hint: Use $gte for start, $lt for end of range [OK]

Common Mistakes:

• Using $gt instead of $gte for lower bound
• Using $gte for upper bound instead of $lt
• Mixing operator directions incorrectly