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$sum
Amazon DocumentDB 中的$sum运算符返回一组中每个文档的指定表达式的总和。它是一个组累加器运算符，通常用于聚合管道的 $group 阶段来执行求和计算。
参数
示例（MongoDB 外壳）
以下示例演示如何使用运$sum算符来计算每种产品的总销售额。
创建示例文档
db.sales.insertMany([
{ product: "abc", price: 10, quantity: 2 },
{ product: "abc", price: 10, quantity: 3 },
{ product: "xyz", price: 20, quantity: 1 },
{ product: "xyz", price: 20, quantity: 5 }
]);
查询示例
db.sales.aggregate([
{ $group: {
_id: "$product",
totalSales: { $sum: { $multiply: [ "$price", "$quantity" ] } }
}}
]);
输出
[
{ "_id": "abc", "totalSales": 50 },
{ "_id": "xyz", "totalSales": 120 }
]
代码示例
要查看使用该$sum命令的代码示例，请选择要使用的语言的选项卡：
- Node.js
-
const { MongoClient } = require('mongodb');
async function example() {
const uri = 'mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false';
const client = new MongoClient(uri);
try {
await client.connect();
const db = client.db('test');
const collection = db.collection('sales');
const result = await collection.aggregate([
{ $group: {
_id: "$product",
totalSales: { $sum: { $multiply: [ "$price", "$quantity" ] } }
}}
]).toArray();
console.log(result);
} catch (error) {
console.error('Error:', error);
} finally {
await client.close();
}
}
example();
- Python
-
from pymongo import MongoClient
from pprint import pprint
def example():
client = None
try:
client = MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
db = client.test
collection = db.sales
result = list(collection.aggregate([
{ '$group': {
'_id': '$product',
'totalSales': { '$sum': { '$multiply': [ '$price', '$quantity' ] } }
}}
]))
pprint(result)
except Exception as e:
print(f"An error occurred: {e}")
finally:
if client:
client.close()
example()
