$bottom

The $bottom operator sorts documents on one or more fields specified by the query and returns the last document matching the filtering criteria.

{
    $bottom: {
        output: [listOfFields],
        sortBy: {
            <fieldName>: < sortOrder >
        }
    }
}

Consider this sample document from the stores collection.

{
    "_id": "0fcc0bf0-ed18-4ab8-b558-9848e18058f4",
    "name": "First Up Consultants | Beverage Shop - Satterfieldmouth",
    "location": {
        "lat": -89.2384,
        "lon": -46.4012
    },
    "staff": {
        "totalStaff": {
            "fullTime": 8,
            "partTime": 20
        }
    },
    "sales": {
        "totalSales": 75670,
        "salesByCategory": [
            {
                "categoryName": "Wine Accessories",
                "totalSales": 34440
            },
            {
                "categoryName": "Bitters",
                "totalSales": 39496
            },
            {
                "categoryName": "Rum",
                "totalSales": 1734
            }
        ]
    },
    "promotionEvents": [
        {
            "eventName": "Unbeatable Bargain Bash",
            "promotionalDates": {
                "startDate": {
                    "Year": 2024,
                    "Month": 6,
                    "Day": 23
                },
                "endDate": {
                    "Year": 2024,
                    "Month": 7,
                    "Day": 2
                }
            },
            "discounts": [
                {
                    "categoryName": "Whiskey",
                    "discountPercentage": 7
                },
                {
                    "categoryName": "Bitters",
                    "discountPercentage": 15
                },
                {
                    "categoryName": "Brandy",
                    "discountPercentage": 8
                },
                {
                    "categoryName": "Sports Drinks",
                    "discountPercentage": 22
                },
                {
                    "categoryName": "Vodka",
                    "discountPercentage": 19
                }
            ]
        },
        {
            "eventName": "Steal of a Deal Days",
            "promotionalDates": {
                "startDate": {
                    "Year": 2024,
                    "Month": 9,
                    "Day": 21
                },
                "endDate": {
                    "Year": 2024,
                    "Month": 9,
                    "Day": 29
                }
            },
            "discounts": [
                {
                    "categoryName": "Organic Wine",
                    "discountPercentage": 19
                },
                {
                    "categoryName": "White Wine",
                    "discountPercentage": 20
                },
                {
                    "categoryName": "Sparkling Wine",
                    "discountPercentage": 19
                },
                {
                    "categoryName": "Whiskey",
                    "discountPercentage": 17
                },
                {
                    "categoryName": "Vodka",
                    "discountPercentage": 23
                }
            ]
        }
    ]
}

Suppose we want to determine the store within the First Up Consultants company with the lowest total sales, run a query to retrieve documents within the First Up Consultants company, sort the documents in descending order of total sales and return the last document in the sorted result set.

db.stores.aggregate([{
    $match: {
        company: {
            $in: ["First Up Consultants"]
        }
    }
}, {
    $group: {
        _id: "$company",
        bottomSales: {
            $bottom: {
                output: ["$company", "$sales"],
                sortBy: {
                    "sales.revenue": -1
                }
            }
        }
    }
}])

This query returns the following result:

[
  {
    "_id": "First Up Consultants",
    "bottomSales": [
        "First Up Consultants",
        {
            "totalSales": 119,
            "salesByCategory": [
                {
                    "categoryName": "Skirts",
                    "totalSales": 109
                }
            ]
        }
    ]
}]

To find the category with the lowest sales per store, run a query to retrieve stores with multiple sales categories, sort the categories in descending order of total sales within each store and return the last document in the sorted result set.

db.stores.aggregate([{
        $unwind: "$sales.salesByCategory"
    },
    {
        $match: {
            "sales.salesByCategory.totalSales": {
                $exists: true
            }
        }
    },
    {
        $group: {
            _id: "$_id",
            storeName: {
                $first: "$name"
            },
            lowestCategory: {
                $bottom: {
                    sortBy: {
                        "sales.salesByCategory.totalSales": 1
                    },
                    output: {
                        categoryName: "$sales.salesByCategory.categoryName",
                        totalSales: "$sales.salesByCategory.totalSales"
                    }
                }
            }
        }
    }
])

The first two results returned by this query are:

[
  {
    "_id": "b1d86d1f-8705-4157-b64c-a9eda0df4921",
    "storeName": "VanArsdel, Ltd. | Baby Products Haven - West Kingfort",
    "lowestCategory": { "categoryName": "Baby Monitors", "totalSales": 49585 }
  },
  {
    "_id": "22e6367e-8341-415f-9795-118d2b522abf",
    "storeName": "Adatum Corporation | Outdoor Furniture Mart - Port Simone",
    "lowestCategory": { "categoryName": "Outdoor Benches", "totalSales": 4976 }
  }
]

• Review options for migrating from MongoDB to Azure Cosmos DB for MongoDB (vCore).
• Read more about feature compatibility with MongoDB.