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# \$1sqrt
<a name="sqrt"></a>

4.0 版的新增内容。

Amazon DocumentDB 中的`$sqrt`运算符用于计算数字的平方根。

**参数**
+ `expression`: 参数可以是任何有效的表达式，只要它解析为非负数即可。

## 示例（MongoDB 外壳）
<a name="sqrt-examples"></a>

以下示例演示如何使用运`$sqrt`算符来计算数字的平方根。

**创建示例文档**

```
db.numbers.insertMany([
  { "_id": 1, "number": 16 },
  { "_id": 2, "number": 36 },
  { "_id": 3, "number": 64 }
]);
```

**查询示例**

```
db.numbers.aggregate([
  { $project: {
    "_id": 1,
    "square_root": { $sqrt: "$number" }
  }}
]);
```

**输出**

```
[
  { _id: 1, square_root: 4 },
  { _id: 2, square_root: 6 },
  { _id: 3, square_root: 8 }
]
```

## 代码示例
<a name="sqrt-code"></a>

要查看使用该`$sqrt`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 client = await MongoClient.connect('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false');

  try {
      await client.connect();

      const db = client.db('test');
      const collection = db.collection('numbers');

      const pipeline = [
        {
          $project: {
            _id: 1,
            square_root: { $sqrt: '$number' }
          }
        }
      ];

      const results = await collection.aggregate(pipeline).toArray();

      console.dir(results, { depth: null });

    } finally {
      await client.close();
    }
}

example().catch(console.error);
```

------
#### [ Python ]

```
from pymongo import MongoClient

def example():
  
  client = MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')

  try:
      db = client.test
      collection = db.numbers

      pipeline = [
          {
              "$project": {
                  "_id": 1,
                  "square_root": { 
                    "$sqrt": "$number" 
                  }
              }
          }
      ]

      results = collection.aggregate(pipeline)

      for doc in results:
          print(doc)

  except Exception as e:
      print(f"An error occurred: {e}")

  finally:
      client.close()

example()
```

------