How does mongodb calculate sum of salary?

Summary: in this tutorial, you’ll learn how to use the MongoDB $sum to return the collective sum of numeric values.

Table of Contents

• Introduction to the MongoDB $sum
• MongoDB $sum examples
• 1) A simple MongoDB $sum example
• 2) Using mongoDB $sum to calculcate the sum of groups
• 3) Using the MongoDB $sum with $sort example
• 4) Using the MongoDB $sum with $match example
• 5) Using the MongoDB $sum with an expression
• How do I sum fields in MongoDB?
• How can you group by a particular value in MongoDB?
• How does MongoDB calculate sum of salary?

Introduction to the MongoDB $sum

MongoDB $sum returns the sum of numeric values. Here’s the syntax of the $sum:

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

Typically, you apply the $sum to the numeric values. However, if a field contains a non-numeric value, the $sum ignores that value. Also, if the field doesn’t exist in any document, the $sum returns 0 for that field.

MongoDB $sum examples

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

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) A simple MongoDB $sum example

The following example calculates the total quantity of coffee sales in the sales collection:

db.sales.aggregate([
  {
    $group: {
      _id: null,
      totalQty: { $sum: '$quantity' },
    },
  },
]);
Code language: PHP (php)

Output:

[ { _id: null, totalQty: 185 } ]
Code language: JavaScript (javascript)

To remove the _id field from the output document, you can use the $project like this:

db.sales.aggregate([
  {
    $group: {
      _id: null,
      totalQty: { $sum: '$quantity' },
    },
  },
  { $project: { _id: 0 } },
]);



Code language: PHP (php)

Output:

[ { totalQty: 185 } ]
Code language: CSS (css)

2) Using mongoDB $sum to calculcate the sum of groups

The following example uses the $sum to calculate the sum of quantity grouped by items:

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

Output:

[
  { _id: 'Cappuccino', totalQty: 49 },
  { _id: 'Lattes', totalQty: 55 },
  { _id: 'Americanos', totalQty: 70 },
  { _id: 'Mochas', totalQty: 11 }
]
Code language: JavaScript (javascript)

In this example, the $group groups the documents by items and the $sum returns the total quantity for each group.

3) Using the MongoDB $sum with $sort example

The following example uses the $sum to returns the total quantity of each item and sorts the result documents by the totalQty in descending order:

db.sales.aggregate([
  {
    $group: {
      _id: '$item',
      totalQty: { $sum: '$quantity' },
    },
  },
  { $sort: { totalQty: -1 } },
]);
Code language: PHP (php)

Output:

[
  { _id: 'Americanos', totalQty: 70 },
  { _id: 'Lattes', totalQty: 55 },
  { _id: 'Cappuccino', totalQty: 49 },
  { _id: 'Mochas', totalQty: 11 }
]
Code language: JavaScript (javascript)

4) Using the MongoDB $sum with $match example

The following example uses the $sum to return the total quantity of each item and $match to include only items with a total quantity greater than 50:

db.sales.aggregate([
  {
    $group: {
      _id: '$item',
      totalQty: { $sum: '$quantity' },
    },
  },
  { $match: { totalQty: { $gt: 50 } } },
  { $sort: { totalQty: -1 } },
]);
Code language: PHP (php)

Output:

[
  { _id: 'Americanos', totalQty: 70 },
  { _id: 'Lattes', totalQty: 55 }
]
Code language: JavaScript (javascript)

5) Using the MongoDB $sum with an expression

The following example uses the $sum to calculate the total amount by multiplying price with quantity for coffee sales group by sizes:

db.sales.aggregate([
  {
    $group: {
      _id: '$size',
      totalAmount: { $sum: { $multiply: ['$price', '$quantity'] } },
    },
  },
  { $sort: { totalAmount: -1 } },
]);
Code language: PHP (php)

Output:

[
  { _id: 'Tall', totalAmount: 1285 },
  { _id: 'Grande', totalAmount: 875 },
  { _id: 'Short', totalAmount: 182 }
]
Code language: JavaScript (javascript)

Summary

• Use MongoDB $sum to return the collective sum of numeric values.
• The $sum ignores numeric values and return 0 for non-existing fields.

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