What does the parameter "select-type=2" mean in SelectObjectContent? Why do we need this?

Question

`select-type` parameter is very confusing. I've tried tweaking aws-cli to generate different values, and it even returns UnauthorizedAccessError.

| Kind | Result |
| --- | --- |
| no `select-type` | UnauthorizedAccessError |
| `select-type=1`| UnauthorizedAccessError |
| `select-type=2` | OK |
| `select-type=3`| UnsupportedCustomerProtocol |

Is it due to some historical reason?

Answer

It is an historical parameter used to define S3 Select response protocol (https://docs.aws.amazon.com/AmazonS3/latest/API/RESTSelectObjectAppendix.html). The only available value for `select-type` is 2.

Answer

I coded this on windows 10 and it worked.  Put your values in for mine.  You will need the s3:GetObject permission on your IAM user to do this command.

aws s3api select-object-content --bucket "bucket-name" --key "key.csv" --expression "select * from s3object" --expression-type "SQL" --input-serialization "{\"CSV\": {}, \"CompressionType\": \"NONE\"}" --output-serialization "{\"CSV\": {}}" outfile.csv

Kind	Result
no `select-type`	UnauthorizedAccessError
`select-type=1`	UnauthorizedAccessError
`select-type=2`	OK
`select-type=3`	UnsupportedCustomerProtocol

What does the parameter "select-type=2" mean in SelectObjectContent? Why do we need this?

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