MongoDB $max

Summary: in this tutorial, you’ll learn how to use the MongoDB $max to return the maximum value.

Introduction to the MongoDB $max

The MongoDB $max returns the maximum value. The $max operator uses both value and type for comparing according to the BSON comparison order for values of different types.

The $max operator has the following syntax:

{ $max: <expression> }
Code language: HTML, XML (xml)

If you apply the $max to the field that has a null or missing value in all documents, the $max returns null.

However, if you apply the $max to the field that has a null or missing value in some documents, but not all, the $max only considers non-null and non-missing values for that field.

MongoDB $max examples

We’ll use the following sales collection to demonstrate the $max:

db.sales.insertMany([
	{ "_id" : 1, "item" : "Americanos", "price" : 5, "size": "Short", "quantity" : 22, "date" : ISODate("2022-01-15T08:00:00Z") },
	{ "_id" : 2, "item" : "Cappuccino", "price" : 6, "size": "Short","quantity" : 12, "date" : ISODate("2022-01-16T09:00:00Z") },
	{ "_id" : 3, "item" : "Lattes", "price" : 15, "size": "Grande","quantity" : 25, "date" : ISODate("2022-01-16T09:05:00Z") },
	{ "_id" : 4, "item" : "Mochas", "price" : 25,"size": "Tall", "quantity" : 11, "date" : ISODate("2022-02-17T08:00:00Z") },
	{ "_id" : 5, "item" : "Americanos", "price" : 10, "size": "Grande","quantity" : 12, "date" : ISODate("2022-02-18T21:06:00Z") },
	{ "_id" : 6, "item" : "Cappuccino", "price" : 7, "size": "Tall","quantity" : 20, "date" : ISODate("2022-02-20T10:07:00Z") },
	{ "_id" : 7, "item" : "Lattes", "price" : 25,"size": "Tall", "quantity" : 30, "date" : ISODate("2022-02-21T10:08:00Z") },
	{ "_id" : 8, "item" : "Americanos", "price" : 10, "size": "Grande","quantity" : 21, "date" : ISODate("2022-02-22T14:09:00Z") },
	{ "_id" : 9, "item" : "Cappuccino", "price" : 10, "size": "Grande","quantity" : 17, "date" : ISODate("2022-02-23T14:09:00Z") },
	{ "_id" : 10, "item" : "Americanos", "price" : 8, "size": "Tall","quantity" : 15, "date" : ISODate("2022-02-25T14:09:00Z")}
]);
Code language: JavaScript (javascript)

1) Using MongoDB $max to find the maximum value example

The following example uses the $max to find the maximum quantity from all the documents:

db.sales.aggregate([
  {
    $group: {
      _id: null,
      maxQty: { $max: '$quantity' },
    },
  },
  {
    $project: {
      _id: 0,
    },
  },
]);
Code language: PHP (php)

Output:

[ { maxQty: 30 } ]
Code language: CSS (css)

2) Using MongoDB $max operator to find the maximum value for each group

The following example uses the $max operator to group documents in the item field and returns the maximum quantity per group of documents:

db.sales.aggregate([
  {
    $group: {
      _id: '$item',
      maxQty: { $max: '$quantity' },
    },
  },
]);
Code language: PHP (php)

Output:

[
  { _id: 'Mochas', maxQty: 11 },
  { _id: 'Americanos', maxQty: 22 },
  { _id: 'Lattes', maxQty: 30 },
  { _id: 'Cappuccino', maxQty: 20 }
]
Code language: JavaScript (javascript)

3) Using MongoDB $max operator example

The following groups the documents by the item field and returns the maximum amount for each group of sales:

db.sales.aggregate([
  {
    $group: {
      _id: '$item',
      maxQty: { $max: { $multiply: ['$quantity', '$price'] } },
    },
  },
]);
Code language: PHP (php)

Output:

[
  { _id: 'Mochas', maxQty: 275 },
  { _id: 'Cappuccino', maxQty: 170 },
  { _id: 'Americanos', maxQty: 210 },
  { _id: 'Lattes', maxQty: 750 }
]
Code language: JavaScript (javascript)

Summary

• Use the MongoDB $max operator to find the maximum value.