Comprehensive MongoDB Command Reference (2026 Edition)

show dbs

Lists all databases in the current MongoDB instance. show dbs Example output:

admin   40.00 KiB
config 108.00 KiB
local   72.00 KiB
order   2.3 GiB
user    1.1 GiB

Useful for quickly viewing the database list.

use

Switches to a specified database; if the database does not exist, it is created on the first write. use order Output: switched to db order Creating a database occurs only after inserting data.

db

Displays the name of the current database. db Output:

order

Commonly used during development and debugging.

show collections

Lists all collections in the current database. show collections Output example:

user
order
product
log

Similar to MySQL's

SHOW TABLES;

db.createCollection

Creates a new collection. db.createCollection("user") Output: { ok : 1 } With options (e.g., capped collection):

db.createCollection("log", { capped: true, size: 104857600 })

Creates a fixed‑size log collection.

db.collection.insertOne

Inserts a single document into a collection.

db.user.insertOne({ name: "Tom", age: 25, city: "Beijing" })

Output:

{ acknowledged: true }

Suitable for adding a single record.

db.collection.insertMany

Inserts multiple documents into a collection.

db.user.insertMany([
  { name: "Tom", age: 20 },
  { name: "Lucy", age: 22 }
])

Output:

{ acknowledged: true }

Useful for initializing data.

db.collection.find

Retrieves documents; without parameters returns all. db.user.find() Formatted output: db.user.find().pretty() Query specific fields: db.user.find({}, { name: 1, age: 1 }) Conditional query example:

db.user.find({ age: 20 })

db.collection.findOne

Returns one matching document. db.user.findOne({ name: "Tom" }) Output example:

{ "_id": "...", "name": "Tom", "age": 20 }

db.collection.updateOne

Modifies a single matching document.

db.user.updateOne({ name: "Tom" }, { $set: { age: 30 } })

Update multiple documents:

db.user.updateMany({}, { $set: { status: 1 } })

db.collection.deleteOne

Removes a single matching document. db.user.deleteOne({ name: "Tom" }) Delete multiple documents with a condition: db.user.deleteMany({ age: { $lt: 18 } }) Delete all documents:

db.user.deleteMany({})

db.collection.countDocuments

Returns the number of documents in a collection. db.user.countDocuments() Conditional count example:

db.user.countDocuments({ age: { $gte: 18 } })

Useful for pagination statistics.

db.collection.createIndex

Creates a standard index. db.user.createIndex({ name: 1 }) Compound index example:

db.order.createIndex({ userId: 1, createTime: -1 })

Unique index example:

db.user.createIndex({ email: 1 }, { unique: true })

View indexes:

db.user.getIndexes()

db.collection.aggregate

Performs advanced data aggregation.

Example – count orders by status:

db.order.aggregate([
  { $group: { _id: "$status", total: { $sum: 1 } } }
])

Example – count documents per age:

db.user.aggregate([
  { $group: { _id: "$age", count: { $sum: 1 } } }
])

db.stats

Shows storage statistics for the current database. db.stats() Typical fields returned: collections, objects, storageSize, indexSize, dataSize.