Filtering and retrieving data using Amazon S3 Select - Amazon Simple Storage Service
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Filtering and retrieving data using Amazon S3 Select

With Amazon S3 Select, you can use structured query language (SQL) statements to filter the contents of an Amazon S3 object and retrieve only the subset of data that you need. By using Amazon S3 Select to filter this data, you can reduce the amount of data that Amazon S3 transfers, which reduces the cost and latency to retrieve this data.

Amazon S3 Select works on objects stored in CSV, JSON, or Apache Parquet format. It also works with objects that are compressed with GZIP or BZIP2 (for CSV and JSON objects only), and server-side encrypted objects. You can specify the format of the results as either CSV or JSON, and you can determine how the records in the result are delimited.

You pass SQL expressions to Amazon S3 in the request. Amazon S3 Select supports a subset of SQL. For more information about the SQL elements that are supported by Amazon S3 Select, see SQL reference for Amazon S3 Select.

You can perform SQL queries using Amazon SDKs, the SelectObjectContent REST API operation, the Amazon Command Line Interface (Amazon CLI), or the Amazon S3 console. The Amazon S3 console limits the amount of data returned to 40 MB. To retrieve more data, use the Amazon CLI or the API.

Requirements and limits

The following are requirements for using Amazon S3 Select:

  • You must have s3:GetObject permission for the object you are querying.

  • If the object you are querying is encrypted with server-side encryption with customer-provided keys (SSE-C), you must use https, and you must provide the encryption key in the request.

The following limits apply when using Amazon S3 Select:

  • The maximum length of a SQL expression is 256 KB.

  • The maximum length of a record in the input or result is 1 MB.

  • Amazon S3 Select can only emit nested data by using the JSON output format.

  • You cannot query objects in the S3 Glacier Flexible Retrieval, S3 Glacier Deep Archive, or Reduced Redundancy Storage (RRS) storage classes. You also cannot query the objects in the S3 Intelligent-Tiering Archive Access tier or the S3 Intelligent-Tiering Deep Archive Access tier. For more information about storage classes, see Using Amazon S3 storage classes.

Additional limitations apply when using Amazon S3 Select with Parquet objects:

  • Amazon S3 Select supports only columnar compression using GZIP or Snappy. Amazon S3 Select doesn't support whole-object compression for Parquet objects.

  • Amazon S3 Select doesn't support Parquet output. You must specify the output format as CSV or JSON.

  • The maximum uncompressed row group size is 512 MB.

  • You must use the data types that are specified in the object's schema.

  • Selecting on a repeated field returns only the last value.

Constructing a request

When you construct a request, you provide details of the object that is being queried by using an InputSerialization object. You provide details of how the results are to be returned by using an OutputSerialization object. You also include the SQL expression that Amazon S3 uses to filter the request.

For more information about constructing an Amazon S3 Select request, see SelectObjectContent in the Amazon Simple Storage Service API Reference. You can also see one of the SDK code examples in the following sections.

Requests using scan ranges

With Amazon S3 Select, you can scan a subset of an object by specifying a range of bytes to query. This capability lets you parallelize scanning the whole object by splitting the work into separate Amazon S3 Select requests for a series of non-overlapping scan ranges.

Scan ranges don't need to be aligned with record boundaries. An Amazon S3 Select scan range request runs across the byte range that you specify. A record that starts within the specified scan range but extends beyond that scan range will be processed by the query. For example, the following shows an Amazon S3 object that contains a series of records in a line-delimited CSV format:

A,B C,D D,E E,F G,H I,J

Suppose that you're using the Amazon S3 Select ScanRange parameter and Start at (Byte) 1 and End at (Byte) 4. So the scan range would start at "," and scan until the end of the record starting at C. Your scan range request will return the result C, D because that is the end of the record.

Amazon S3 Select scan range requests support Parquet, CSV (without quoted delimiters), and JSON objects (in LINES mode only). CSV and JSON objects must be uncompressed. For line-based CSV and JSON objects, when a scan range is specified as part of the Amazon S3 Select request, all records that start within the scan range are processed. For Parquet objects, all of the row groups that start within the scan range requested are processed.

Amazon S3 Select scan range requests are available to use with the Amazon CLI, Amazon S3 API, and Amazon SDKs. You can use the ScanRange parameter in the Amazon S3 Select request for this feature. For more information, see SelectObjectContent in the Amazon Simple Storage Service API Reference.

Errors

Amazon S3 Select returns an error code and associated error message when an issue is encountered while attempting to run a query. For a list of error codes and descriptions, see the List of SELECT Object Content Error Codes section of the Error Responses page in the Amazon Simple Storage Service API Reference.

For more information about Amazon S3 Select, see the following topics.