$max
The $max operator returns the maximum value from a set of input values.
$max
The $max operator returns the maximum value of a set of input values.
When used as a field update operator, the $max operator updates the value of a field to a specified value if the specified value is greater than the current value of the field. If the field does not exist, $max creates the field and sets it to the specified value.
Syntax
$max: <expression>When used as a field update operator:
{
$max: {
<field1>: <value1>,
<field2>: <value2>,
...
}
}Parameters
| Parameter | Description |
|---|---|
<expression> | Any valid expression that resolves to a value. The $max operator evaluates this expression to determine the maximum value. |
When used as a field update operator:
| Parameter | Description |
|---|---|
field | The name of the field to update with the maximum value. |
value | The value to compare with the current field value. The field will be updated only if this value is larger. |
Examples
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
}
]
}
]
}Example 1: Calculate the highest sales by category
To calculate the highest sales within each category, first run a query to group all documents by sales category. Then run a $max query to retrieve the highest sales within each category across all stores.
db.stores.aggregate([{
$unwind: "$sales.salesByCategory"
},
{
$group: {
_id: "$sales.salesByCategory.categoryName",
maxSales: {
$max: "$sales.salesByCategory.totalSales"
}
}
}
])The first five results returned by this query are:
[
{
"_id": "Christmas Trees",
"maxSales": 49697
},
{
"_id": "Nuts",
"maxSales": 48020
},
{
"_id": "Camping Tables",
"maxSales": 48568
},
{
"_id": "Music Theory Books",
"maxSales": 46133
},
{
"_id": "Fortified Wine",
"maxSales": 49912
}
]Example 2: Using $max in $bucket
To retrieve the highest sales within buckets of sales boundaries:
db.stores.aggregate([{
$bucket: {
groupBy: "$sales.totalSales",
boundaries: [0, 1000, 5000, 10000],
default: "Other",
output: {
maxSales: {
$max: "$sales.totalSales"
}
}
}
}])This query returns the following results:
[
{
"_id": 1000,
"maxSales": 4996
},
{
"_id": "Other",
"maxSales": 404106
},
{
"_id": 0,
"maxSales": 995
},
{
"_id": 5000,
"maxSales": 9999
}
]Example 3: Using $max in $setWindowFields
To get the highest discount for laptops in 2023, first run a query to unwind just promotion events and filter on the chosen category. Then partition the resulting documents by company and calculate the highest discount percentage within each resulting partition.
db.stores.aggregate([{
$unwind: "$promotionEvents"
},
{
$unwind: "$promotionEvents.discounts"
},
// Filter only Laptops category and events in 2023
{
$match: {
"promotionEvents.promotionalDates.startDate.Year": 2023,
"promotionEvents.discounts.categoryName": "Laptops"
}
},
// Use $setWindowFields to calculate average discount by city
{
$setWindowFields: {
partitionBy: "$company",
output: {
maxDiscount: {
$max: "$promotionEvents.discounts.discountPercentage",
window: {
documents: ["unbounded", "unbounded"]
}
}
}
}
},
// Group by city to return one result per city
{
$group: {
_id: "$company",
maxDiscount: {
$first: "$maxDiscount"
}
}
}
])The first three results returned by this query are:
[
{
"_id": "Proseware, Inc.",
"maxDiscount": 24
},
{
"_id": "Fabrikam, Inc.",
"maxDiscount": 23
},
{
"_id": "Contoso, Ltd.",
"maxDiscount": 24
}
]Example 4: Setting maximum staff capacity (field update operator)
To update the full time staff to 10 only if the current full time staff count is lower, use the $max operator on the field to perform the update. Since the current fullTime value is 3, and 10 is greater than 3, the field will be updated to 10.
db.stores.updateOne(
{ _id: "f2a8c190-28e4-4e14-9d8b-0256e53dca66" },
{
$max: {
"staff.totalStaff.fullTime": 10
}
}
)Example 5: Multiple field updates (field update operator)
To update multiple fields with maximum values, use the $max operator with multiple fields and their corresponding max values to set.
db.stores.updateOne(
{ _id: "f2a8c190-28e4-4e14-9d8b-0256e53dca66" },
{
$max: {
"staff.totalStaff.partTime": 1,
"sales.totalSales": 50000
}
}
)In this case:
partTime(2) will remain 2 since 1 < 2 (no change)totalSales(31211) will be updated to 50000 since 50000 > 31211
Example 6: Creating new fields (field update operator)
If a field doesn't exist, $max creates it with the specified value.
db.stores.updateOne(
{ _id: "f2a8c190-28e4-4e14-9d8b-0256e53dca66" },
{
$max: {
"staff.maxStaffCapacity": 25,
"sales.peakSalesRecord": 100000
}
}
)Example 7: Updating array elements (field update operator)
Update maximum values within array elements using positional operators.
db.stores.updateOne(
{
_id: "f2a8c190-28e4-4e14-9d8b-0256e53dca66",
"sales.salesByCategory.categoryName": "Phone Mounts"
},
{
$max: {
"sales.salesByCategory.$.totalSales": 12000
}
}
)Example 8: Tracking peak performance (field update operator)
Set peak performance metrics that only update when exceeded.
db.stores.updateOne(
{ _id: "f2a8c190-28e4-4e14-9d8b-0256e53dca66" },
{
$max: {
"performance.peakDailySales": 5000,
"performance.maxCustomersPerDay": 150,
"performance.highestSalesMonth": 45000
}
}
)After these field update operations, the updated document is:
{
"_id": "f2a8c190-28e4-4e14-9d8b-0256e53dca66",
"name": "Fabrikam, Inc. | Car Accessory Outlet - West Adele",
"staff": {
"totalStaff": {
"fullTime": 10,
"partTime": 2
},
"maxStaffCapacity": 25
},
"sales": {
"totalSales": 50000,
"peakSalesRecord": 100000,
"salesByCategory": [
{
"categoryName": "Phone Mounts",
"totalSales": 12000
},
{
"categoryName": "Dash Cameras",
"totalSales": 22300
}
]
},
"performance": {
"peakDailySales": 5000,
"maxCustomersPerDay": 150,
"highestSalesMonth": 45000
},
"lastPromotionDate": ISODate("2024-12-31T00:00:00.000Z"),
"inventoryDeadline": ISODate("2024-06-30T00:00:00.000Z")
}