Step 1: Switch to the Database

Before running queries, ensure you’re using the correct database.

use myDatabase

Step 2: View Sample Data

Let’s assume we have a users collection with the following documents:

db.users.find().pretty()

Sample Data:

[
  { "_id": 1, "name": "Alice", "age": 28, "city": "New York" },
  { "_id": 2, "name": "Bob", "age": 34, "city": "Los Angeles" },
  { "_id": 3, "name": "Charlie", "age": 23, "city": "Chicago" },
  { "_id": 4, "name": "David", "age": 30, "city": "New York" }
]

Step 3: Using Comparison Operators

Comparison operators filter data based on specific conditions.

1. $gt (Greater Than)

Find users older than 25:

db.users.find({ age: { $gt: 25 } })

✅ Returns users with age greater than 25.

2. $lt (Less Than)

Find users younger than 30:

db.users.find({ age: { $lt: 30 } })

✅ Returns users with age less than 30.

3. $gte & $lte (Greater/Less Than or Equal)

Find users aged between 25 and 30:

db.users.find({ age: { $gte: 25, $lte: 30 } })

Step 4: Using Logical Operators

Logical operators combine multiple conditions.

1. $and Operator

Find users from New York who are older than 25:

db.users.find({ $and: [{ city: "New York" }, { age: { $gt: 25 } }] })

✅ Returns users from New York with age greater than 25.

2. $or Operator

Find users who are either from New York or Chicago:

db.users.find({ $or: [{ city: "New York" }, { city: "Chicago" }] })

✅ Returns users from New York OR Chicago.

3. $not Operator

Find users not from Los Angeles:

db.users.find({ city: { $not: { $eq: "Los Angeles" } } })

db.users.find({ city: { $exists: true } })

db.users.find({ age: { $type: "int" } })

db.users.find().pretty()