S3 Select CSV Headers

Question

我正在使用 S3 Select 从 S3 存储桶读取 csv 文件并输出为 CSV。在输出中我只看到行，但看不到 headers。如何获得包含 headers 的输出。

import boto3

s3 = boto3.client('s3')

r = s3.select_object_content(
        Bucket='demo_bucket',
        Key='demo.csv',
        ExpressionType='SQL',
        Expression="select * from s3object s",
        InputSerialization={'CSV': {"FileHeaderInfo": "Use"}},
        OutputSerialization={'CSV': {}},
)

for event in r['Payload']:
    if 'Records' in event:
        records = event['Records']['Payload'].decode('utf-8')
        print(records)

CSV

Name, Age, Status
Rob, 25, Single
Sam, 26, Married

s3select 的输出

Rob, 25, Single
Sam, 26, Married

Answer 1

Amazon S3 Select 不会输出 headers.

在您的代码中，您可以只包含 print 命令以在循环结果之前输出 headers。

Answer 2

改变InputSerialization={'CSV': {"FileHeaderInfo": "Use"}},

TO InputSerialization={'CSV': {"FileHeaderInfo": "NONE"}},

然后，它将打印全部内容，包括header。

解释:

FileHeaderInfo 接受 "NONE|USE|IGNORE".

之一

使用 NONE 选项而不是 USE，然后它也会打印 header，因为 NONE 告诉您还需要 header处理中。

这里是参考。 https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/s3.html#S3.Client.select_object_content

希望对您有所帮助。

Answer 3

Red Boy 的解决方案不允许您在查询中使用列名，而是必须使用列索引。这对我不利，所以我的解决方案是执行另一个查询以仅获取 headers 并将它们与实际查询结果连接起来。这是在 JavaScript 但同样适用于 Python:

      const params = {
        Bucket: bucket,
        Key: "file.csv",
        ExpressionType: 'SQL',
        Expression: `select * from s3object s where s."date" >= '${fromDate}'`,
        InputSerialization: {'CSV': {"FileHeaderInfo": "USE"}},
        OutputSerialization: {'CSV': {}},
      };

      //s3 select doesn't return the headers, so need to run another query to only get the headers (see '{"FileHeaderInfo": "NONE"}')
      const headerParams = {
        Bucket: bucket,
        Key: "file.csv",
        ExpressionType: 'SQL',
        Expression: "select * from s3object s limit 1", //this will only get the first record of the csv, and since we are not parsing headers, they will be included
        InputSerialization: {'CSV': {"FileHeaderInfo": "NONE"}},
        OutputSerialization: {'CSV': {}},
      };

      //concatenate header + data -- getObject is a method that handles the request
      return await this.getObject(s3, headerParams) + await this.getObject(s3, params);

S3 Select CSV Headers

S3 Select CSV Headers

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