MongoDB $second Operator

Example 1 — Sample Data

Imagine two sales with precise timestamps. We save them in a collection named sales.

db.sales.insertMany([
  {
    _id: 1,
    item: "abc",
    price: 10,
    quantity: 2,
    date: ISODate("2014-01-01T08:15:39.736Z")
  },
  {
    _id: 2,
    item: "xyz",
    price: 20,
    quantity: 1,
    date: ISODate("2016-01-01T12:01:00.000Z")
  }
]);

How the Data Is Stored in MongoDB

After the insert, MongoDB keeps two documents in sales. Run find() to see them:

db.sales.find()

[
  {
    _id: 1,
    item: "abc",
    price: 10,
    quantity: 2,
    date: ISODate("2014-01-01T08:15:39.736Z")
  },
  {
    _id: 2,
    item: "xyz",
    price: 20,
    quantity: 1,
    date: ISODate("2016-01-01T12:01:00.000Z")
  }
]

Read one document like this:

How It Works

1. Insert once. insertMany adds two sale documents to sales.
2. Dates are BSON Date. Use ISODate(...), not plain strings.
3. find() shows the same shape. Ready for $second next.

Example 2 — Extract Seconds

Goal: read the 0–59 seconds portion of each sale’s date (UTC).

db.sales.aggregate([
  {
    $addFields: {
      seconds: { $second: "$date" }
    }
  }
]);

{
  _id: 1,
  item: "abc",
  price: 10,
  quantity: 2,
  date: ISODate("2014-01-01T08:15:39.736Z"),
  seconds: 39
}
{
  _id: 2,
  item: "xyz",
  price: 20,
  quantity: 1,
  date: ISODate("2016-01-01T12:01:00.000Z"),
  seconds: 0
}

How It Works

1. Read the stored date. Document 1 has …T08:15:39.736Z.
2. Extract seconds. $second: "$date" returns 39 (UTC).
3. Second document. …T12:01:00Z → second 0.
4. Keep all fields. $addFields adds seconds next to the original sale data.

Example 3 — Hour, Minute, Second

Same sales, but project the full clock parts together so you can see how $second fits next to hour and minute.

db.sales.aggregate([
  {
    $project: {
      item: 1,
      hour: { $hour: "$date" },
      minute: { $minute: "$date" },
      second: { $second: "$date" }
    }
  }
]);

{
  _id: 1,
  item: "abc",
  hour: 8,
  minute: 15,
  second: 39
}
{
  _id: 2,
  item: "xyz",
  hour: 12,
  minute: 1,
  second: 0
}

How It Works

1. Same stored dates. Still using the two sales from Example 1.
2. Split the clock. $hour, $minute, and $second each return one integer part (UTC).
3. First sale. 08:15:39 → hour 8, minute 15, second 39.
4. Second sale. 12:01:00 → hour 12, minute 1, second 0.