该 $round 运算符用于将数字舍入到指定的小数位。 它在数值精度非常重要的聚合中非常有用，例如财务计算或统计分析。
{
$round: [ <number>, <place> ]
}
| 参数 | DESCRIPTION |
|---|---|
<number> |
要舍入的数字。 |
<place> |
数字应舍入到的小数位数。 |
请考虑存储集合中的此示例文档。
{
"_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
}
]
}
]
}
若要对“第一次咨询”公司内所有商店的纬度和经度进行四舍五入，请先运行查询以筛选公司名称。 然后，使用 lat 和 lon 字段上的 $round 运算符返回所需的结果。
db.stores.aggregate([{
"$match": {
"company": {
"$in": [
"First Up Consultants"
]
}
}
}, {
"$project": {
"company": 1,
"location.lat": 1,
"location.lon": 1,
"roundedLat": { $round: ["$location.lat", 1] },
"roundedLon": { $round: ["$location.lon", 1] }
}
}])
此查询返回的前三个结果为：
[
{
"_id": "39acb3aa-f350-41cb-9279-9e34c004415a",
"location": {
"lat": 87.2239,
"lon": -129.0506
},
"company": "First Up Consultants",
"roundedLat": 87.2,
"roundedLon": -129.1
},
{
"_id": "26afb024-53c7-4e94-988c-5eede72277d5",
"location": {
"lat": -29.1866,
"lon": -112.7858
},
"company": "First Up Consultants",
"roundedLat": -29.2,
"roundedLon": -112.8
},
{
"_id": "62438f5f-0c56-4a21-8c6c-6bfa479494ad",
"location": {
"lat": -0.2136,
"lon": 108.7466
},
"company": "First Up Consultants",
"roundedLat": -0.2,
"roundedLon": 108.7
}
]
若要舍入“第一向上顾问”公司内商店的总销售量，请首先运行查询以按公司名称筛选商店。 然后使用 totalSales 字段上的 $round 运算符将值舍入到最接近的千。
db.stores.aggregate([{
"$match": {
"company": {
"$in": ["First Up Consultants"]
}
}
}, {
"$project": {
"company": 1,
"sales.totalSales": 1,
"roundedSales": {
$round: ["$sales.totalSales", -3]
}
}
}])
此查询返回的前三个结果为：
[
{
"_id": "39acb3aa-f350-41cb-9279-9e34c004415a",
"sales": {},
"company": "First Up Consultants",
"roundedSales": 279000
},
{
"_id": "26afb024-53c7-4e94-988c-5eede72277d5",
"sales": {},
"company": "First Up Consultants",
"roundedSales": 50000
},
{
"_id": "62438f5f-0c56-4a21-8c6c-6bfa479494ad",
"sales": {},
"company": "First Up Consultants",
"roundedSales": 69000
}
]