# MongoDB Command Quick Reference

## Database & Collection

```javascript
use myDatabase              // switch/create database
show collections            // list collections
db.createCollection('users')
```

## Insert

```javascript
db.users.insertOne({ name: 'Alice', age: 30 })
db.users.insertMany([{ name: 'Bob' }, { name: 'Carol' }])
```

## Find (Read)

```javascript
db.users.find()                          // all documents
db.users.find({ age: { $gt: 18 } })      // filter
db.users.findOne({ name: 'Alice' })      // single document
db.users.find().sort({ age: -1 })        // sort descending
db.users.find().limit(10)
```

## Update

```javascript
db.users.updateOne({ name: 'Alice' }, { $set: { age: 31 } })
db.users.updateMany({ age: { $lt: 18 } }, { $set: { status: 'minor' } })
```

## Delete

```javascript
db.users.deleteOne({ name: 'Alice' })
db.users.deleteMany({ status: 'inactive' })
```

## Aggregation Pipeline

```javascript
db.orders.aggregate([
  { $match: { status: 'completed' } },
  { $group: { _id: '$category', total: { $sum: '$amount' } } },
  { $sort: { total: -1 } }
])
```

## Common Mistakes

- updateOne/deleteOne ကို updateMany/deleteMany လိုချင်တဲ့အခါ သုံးမိခြင်း — document တစ်ခုပဲ ထိမည်
- Filter query မပါဘဲ deleteMany({}) run ခြင်း — collection ထဲ document အားလုံး ဖျက်ပါလိမ့်မယ်