MongoDB $sqrt Operator

What is the $sqrt operator in MongoDB?

MongoDB provides a variety of arithmetic expression operators. The $sqrt operator is one of those arithmetic expression operators. The $sqrt operator is used to calculate the square root of a positive number, and it returns the output as a double. This operator is also used in the aggregation pipeline stages.

Syntax of the $sqrt operator:

The < number > can be any valid number as long as it resolves for a non-negative number.

Important point:

If the number refers to a missing field or null, the $sqrt operator returns the null.
If the number is NaN, the $sqrt operator returns NaN.

S.No	Example	Output
1.	{ $sqrt: 4 }	2
2.	{ $sqrt: 15 }	3.872983346207417
3.	{ $sqrt: -2 }	Error
4.	{ $sqrt: null}	Null

Examples:

Suppose we have a collection of items with the following documents.

>db.items.find().pretty()
{
        {
         "_id" : 1, 
         "item_name" : "bat",
         "quantity" : 4
        }
        {
         "_id" : 2, 
         "item_name" : "ball",
         "quantity" : null
        }
        {
         "_id" : 3, 
         "item_name" : "box",
         "details" : { 
                           "length" : 20,
                           "width" : 25
                          }
        }
        {
         "_id" : 4, 
         "item_name" : "ball",
         "quantity" : null
        }
        {
         "_id" : 5, 
         "item_name" : "bat",
         "quantity" : 20
        }
        {
         "_id" : 6, 
         "item_name" : "toy",
         "quantity" : -10
        }
        {
         "_id" : 7, 
         "item_name" : "bat",
         "quantity" : 75
        }
        {
         "_id" : 8, 
         "item_name" : "bat",
         "quantity" : 45
        }
}

Example 1: Using $sqrt operator to finding the square root of any field

In this example, we are using the $sqrt operator to find the square root of the "quantity" field.

db.items.aggregate(
 [
   {$match: { item_name : "bat"}},
      {
          $project: 
              {
                item_name : 1,
                quantity : 1,
                result : {$sqrt: "$quantity" }
               }
      }
 ]
)

Output:

{
         "_id" : 1, 
         "item_name" : "bat",
         "quantity" : 4,
         "result" : 2
}
{
         "_id" : 5, 
         "item_name" : "bat",
         "quantity" : 20,
         "result" : 4.472135954999579
}
{
         "_id" : 7, 
         "item_name" : "bat",
         "quantity" : 75,
         "result" : 8.660254037844386
}
{
         "_id" : 8, 
         "item_name" : "bat",
         "quantity" : 45,
         "result" : 6.708203932499369
}

Example 2: Negative values of the field

The $sqrt operator only supports positive numbers that must be greater than or equal to 0. If the value of the argument is negative, it gives an error. Let's apply the $sqrt operator against the toy documents.

db.items.aggregate(
 [
   {$match: { item_name : "toy"}},
      {
          $project: 
              {
                item_name : 1,
                quantity : 1,
                result : {$sqrt: "$quantity" }
               }
      }
 ]
)

Output:

uncaught exception: Error: command failed: {
	"ok": 0,
	"errmsg": "$sqrt's argument must be greater than or equal to 0",
	"code": 28714,
	"codeName": "Location28714"
} : aggregate failed:
_getErrorWithCode@src/mongo/shell/utils.js : 25 : 13
doassert@src/mongo/shell/assert.js : 18 : 14
_assertCommandWorked@src/mongo/shell/assert.js : 618 : 17
assert.commandWorked@src/mongo/shell/assert.js : 708 : 16
DB.prototype._runAggregate@src/mongo/shell/db.js : 266 :5
DBCollection.prototype.aggregate@src/mongo/shell/collection.js : 1046 : 12
@(shell) : 1 : 1

Example 3: Null values of the field

If the field value is null, the $sqrt operator returns the null. Let's apply the $sqrt operator against the ball documents.

db.items.aggregate(
 [
   {$match: { item_name : "ball"}},
      {
          $project: 
              {
                item_name : 1,
                quantity : 1,
                result : {$sqrt: "$quantity" }
               }
      }
 ]
)

Output:

{
         "_id" : 2, 
         "item_name" : "ball",
         "quantity" : null,
         "result" : null
}
{
         "_id" : 4, 
         "item_name" : "ball",
         "quantity" : null,
         "result" : null
}

Example 4: Non-existent Fields

If the argument refers to a missing field, the $sqrt operator returns the null. In this example, we are using the $sqrt operator to find the square root of the "price" field.

db.items.aggregate(
 [
   {$match: { _id : 5}},
      {
          $project: 
              {
                item_name : 1,
                quantity : 1,
                result : {$sqrt: "$price" }
               }
      }
 ]
)

Output:

{
         "_id" : 5, 
         "item_name" : "bat",
         "quantity" : 20,
         "result" : null
}

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MongoDB $sqrt Operator

What is the $sqrt operator in MongoDB?

Syntax of the $sqrt operator:

Examples:

Example 4: Non-existent Fields

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