Introduction to MongoDB $sqrt Operator

The $sqrt operator is a mathematical operator in MongoDB used to calculate the square root of a given number. It can be used as part of the aggregation pipeline to perform mathematical calculations and transformations on data.

Syntax

The syntax for the $sqrt operator is as follows:

{ $sqrt: <number> }

Here, <number> is the number for which the square root is to be calculated, which can be any numeric field or constant.

Use Cases

The $sqrt operator can be used at any stage in the aggregation pipeline to calculate the square root of a numeric field. For example, in some scenarios, it may be necessary to calculate the average age of users or the standard deviation of certain metrics. In these cases, using the $sqrt operator can make the calculation more convenient.

Examples

Here are two examples of using the $sqrt operator:

Example 1

Suppose there is a collection users that contains the name, age, and income of each user. Now, we want to calculate the average age and standard deviation of all users. We can use the following aggregation pipeline to accomplish this:

db.users.aggregate([
  {
    $group: {
      _id: null,
      avgAge: { $avg: "$age" },
      stdAge: {
        $sqrt: {
          $avg: { $pow: ["$age", 2] },
          $avg: "$age"
        }
      }
    }
  }
])

This aggregation pipeline uses the $avg operator to calculate the average age and the $pow operator to calculate the square of the age. Then, the $sqrt operator is used to calculate the standard deviation.

Example 2

Suppose there is a collection products that contains the name, price, and sales of each product. Now, we want to query the average price and standard deviation of products with a price greater than 100 and sales greater than 1000. We can use the following aggregation pipeline to accomplish this:

db.products.aggregate([
  {
    $match: {
      price: { $gt: 100 },
      sales: { $gt: 1000 }
    }
  },
  {
    $group: {
      _id: null,
      avgPrice: { $avg: "$price" },
      stdPrice: {
        $sqrt: {
          $avg: { $pow: ["$price", 2] },
          $avg: "$price"
        }
      }
    }
  }
])

This aggregation pipeline uses the $match operator to filter products with a price greater than 100 and sales greater than 1000. Then, the $avg operator is used to calculate the average price and the $pow operator is used to calculate the square of the price. Finally, the $sqrt operator is used to calculate the standard deviation of the price.