Introduction to MongoDB $second Operator

$second is one of the date operators in MongoDB used to handle datetime types. It extracts the second value from a specified date and can be used in aggregation operations.


The syntax of the $second operator is as follows:

{ $second: <dateExpression> }

Here, <dateExpression> is an expression that can be a field reference, a constant value, or another expression.

Use Cases

The $second operator is typically used in aggregation operations and can be used to group, filter, and sort based on the seconds in a datetime. For example, we can use $second to find the amount of data generated per minute during a certain time period, or to find the busiest hour of a day.


Suppose we have a collection orders containing the following documents:

{ _id: 1, date: ISODate("2022-03-07T10:15:30Z") }
{ _id: 2, date: ISODate("2022-03-07T10:25:30Z") }
{ _id: 3, date: ISODate("2022-03-07T11:15:30Z") }
{ _id: 4, date: ISODate("2022-03-07T11:25:30Z") }

To aggregate data by seconds, we can use the following pipeline:

    $group: {
      _id: { $second: "$date" },
      count: { $sum: 1 }
  { $sort: { _id: 1 } }

In this pipeline, the $group operator aggregates the date field by second. Then, the $sort operator sorts by second to better visualize the data.

After executing the aggregation, the following result is returned:

{ "_id" : 30, "count" : 2 }
{ "_id" : 15, "count" : 2 }

This indicates that there are 2 documents in the orders collection with a second value of 30 in their dates, and 2 documents with a second value of 15.


The $second operator is one of the available date operators in MongoDB that can be used to extract seconds from a date field. It is applicable to a variety of use cases, such as calculating the number of seconds an event occurs in a day, aggregating data by seconds to generate reports, and more. By using the $second operator, working with and manipulating documents containing date fields can be made easier, allowing for better management and analysis of data.