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Day 02 Core Concepts

Queries and Operators

Comparison, logical, and array operators. Projection, sort, skip, and limit.

~1 hour Hands-on Precision AI Academy

Today’s Objective

Comparison, logical, and array operators. Projection, sort, skip, and limit.

Queries and Operators is one of the most important topics in MongoDB in 5 Days. This lesson builds the foundation you need before moving to more advanced concepts — take time with each example and run the code yourself.

Query Operators

Comparison Operators
COMPARISON OPERATORS
// Numeric comparisons
db.products.find({ price: { $gt: 100 } }) // > 100
db.products.find({ price: { $gte: 100 } }) // >= 100
db.products.find({ price: { $lt: 50 } }) // < 50
db.products.find({ price: { $ne: 0 } }) // != 0
db.products.find({ category: { $in: ['Electronics', 'Books'] } })
db.products.find({ category: { $nin: ['Food'] } })
Logical Operators
LOGICAL OPERATORS
// AND (implicit — just combine conditions)
db.products.find({ price: { $lt: 100 }, inStock: true })

// Explicit AND
db.products.find({ $and: [ { price: { $lt: 100 } }, { category: 'Electronics' }
]})

// OR
db.products.find({ $or: [ { price: { $lt: 10 } }, { featured: true }
]})

// NOT
db.products.find({ category: { $not: { $eq: 'Food' } } })
Projection, Sort, Limit
PROJECTION, SORT, LIMIT
// Projection: 1 = include, 0 = exclude
db.products.find({}, { name: 1, price: 1, _id: 0 })

// Sort: 1 = ascending, -1 = descending
db.products.find().sort({ price: -1 })

// Pagination
const PAGE = 2;
const PER_PAGE = 10;
db.products.find() .sort({ createdAt: -1 }) .skip((PAGE - 1) * PER_PAGE) .limit(PER_PAGE)
📝 Day 2 Exercise
Build Pagination
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Supporting Resources

Go deeper with these references.

MongoDB Docs
Official MongoDB Manual Complete reference documentation for all MongoDB features and operations.
→
MongoDB University
Free MongoDB Courses Official free courses on MongoDB fundamentals, aggregation, and performance.
→
GitHub
MongoDB Driver Examples Official Node.js and Python driver examples on GitHub.
→

Day 2 Checkpoint

Before moving on, make sure you can answer these without looking:

Continue To Day 3
Aggregation Pipelines
→