mongosh Basics — connect, show dbs, use db

What is mongosh?

mongosh (MongoDB Shell) is the official interactive command-line interface for MongoDB. Think of it as your direct conversation with the database — you type commands, it responds with data.

SQL World	MongoDB World
`mysql` CLI	`mongosh`
`sqlcmd` (SQL Server)	`mongosh`
`psql` (PostgreSQL)	`mongosh`

            mongosh is a full JavaScript REPL. That means you can use variables, loops, functions — real JavaScript — right inside the shell. This is way more powerful than a typical SQL CLI.
        

Connecting to MongoDB

Default Local Connection

If MongoDB is running locally on the default port, just type:

mongosh

This is shorthand for:

mongosh "mongodb://localhost:27017"

Connection String Anatomy

mongodb://  localhost  :  27017  /  myDatabase
────────    ─────────    ─────     ──────────
protocol    host         port      database (optional)

Connect to a Specific Database Directly

// Connects and switches to "myShop" immediately
mongosh "mongodb://localhost:27017/myShop"

Connection with Authentication

// When your server requires a username/password
mongosh "mongodb://localhost:27017" --username [user] --password [pass]

// Or in the connection string
mongosh "mongodb://[user]:[pass]@localhost:27017/admin"

✅ When connected, you'll see a prompt like:
test> or myShop> — this shows which database you're currently using.

Essential Navigation Commands

These are the commands you'll use constantly. Here's the SQL equivalent for each:

show dbs — List All Databases

test> show dbs

// Output:
// admin    40.00 KiB
// config  108.00 KiB
// local    40.00 KiB

MongoDB	SQL Equivalent
`show dbs`	`SHOW DATABASES;` (MySQL) or query `sys.databases` (SQL Server)

⚠️ Note: A database won't appear in show dbs until it has at least one document in it. Creating a database with use alone isn't enough — it's "lazy created."

use — Switch to a Database

test> use myShop
// Output: switched to db myShop

myShop>

If the database doesn't exist yet, MongoDB doesn't complain — it just creates it when you first insert data. No CREATE DATABASE needed.

MongoDB	SQL Equivalent
`use myShop`	`USE myShop;` (MySQL) or `USE [myShop];` (SQL Server)

db — Show Current Database

myShop> db
// Output: myShop

MongoDB	SQL Equivalent
`db`	`SELECT DATABASE();` (MySQL) or `SELECT DB_NAME();` (SQL Server)

show collections — List Collections in Current DB

myShop> show collections

// Output:
// products
// orders
// customers

MongoDB	SQL Equivalent
`show collections`	`SHOW TABLES;` (MySQL) or query `sys.tables` (SQL Server)

Quick Data Commands (Preview)

You'll learn these in depth later, but here's a taste so you can experiment in the shell right now:

// Switch to a practice database
use practice

// Insert a document (creates the collection automatically)
db.users.insertOne({
  name: "Alex",
  age: 28,
  role: "developer"
})

// Find all documents in the collection
db.users.find()

// Find with a filter (like WHERE)
db.users.find({ role: "developer" })

// Count documents
db.users.countDocuments()

// Drop the collection when done experimenting
db.users.drop()

// Drop the entire database
db.dropDatabase()

            Key insight: In MongoDB, you never need to "create" a database or collection upfront. Just use a database and insertOne() into a collection — both are created automatically on first write. This is very different from SQL where you must CREATE DATABASE and CREATE TABLE first.
        

Helpful mongosh Features

Tab Completion

Type db. and press Tab — mongosh will show you all available methods. Works for collection names too.

Command History

Press ↑ and ↓ arrow keys to cycle through previous commands, just like any terminal.

Multi-line Input

mongosh automatically detects incomplete expressions. If you open a { and press Enter, it waits for the closing }:

myShop> db.users.insertOne({
...   name: "Sam",
...   age: 32
... })

Built-in Help

// General help
help

// Database-level help
db.help()

// Collection-level help
db.users.help()

.editor Mode

For longer commands, enter editor mode:

myShop> .editor
// Entering editor mode (Ctrl+D to finish, Ctrl+C to cancel)

db.products.insertMany([
  { name: "Laptop", price: 999, category: "electronics" },
  { name: "Mouse", price: 29, category: "electronics" },
  { name: "Desk", price: 250, category: "furniture" }
])

// Press Ctrl+D to execute

Clear the Screen

cls
// or
console.clear()

Exit mongosh

exit
// or
quit
// or press Ctrl+C twice

📋 mongosh Quick Reference

Command	What It Does	SQL Equivalent
`mongosh`	Connect to local MongoDB	Open SQL CLI
`show dbs`	List all databases	`SHOW DATABASES`
`use myDb`	Switch to / create database	`USE myDb` / `CREATE DATABASE`
`db`	Show current database name	`SELECT DATABASE()`
`show collections`	List collections in current db	`SHOW TABLES`
`db.col.find()`	Show all documents	`SELECT * FROM col`
`db.col.insertOne({...})`	Insert one document	`INSERT INTO col ...`
`db.col.countDocuments()`	Count documents	`SELECT COUNT(*) FROM col`
`db.col.drop()`	Delete a collection	`DROP TABLE col`
`db.dropDatabase()`	Delete current database	`DROP DATABASE`

🏋️ Try It Yourself

Open mongosh and complete these exercises:

Exercise 1: List all databases. How many do you see?

Exercise 2: Create a database called playground and insert this document into a notes collection:

{ title: "My first note", content: "Learning mongosh!", createdAt: new Date() }

Exercise 3: Run show dbs — does playground appear now?

Exercise 4: Run db.notes.find() to see your document. Notice the _id field that MongoDB added automatically.

Exercise 5: Clean up — drop the playground database with db.dropDatabase().

🧠 Quick Check

Test yourself:

1. What command lists all databases in MongoDB?

2. What happens when you run use newDb and newDb doesn't exist?

3. When does a new database first appear in show dbs?

4. What language does mongosh use under the hood?

💻 mongosh Basics