SELECT Object Content

Overview

This API (COS Select) is used to extract the content from the specified object (in CSV or JSON format) using Structured Query Language (SQL) statements. During the extraction process, you need to specify the content delimiter and use an appropriate SQL function. COS Select will return the matching extraction result, and you can specify the save format of the result.

For more information on COS Select, see COS Select Overview. For more information on the SQL expressions of COS Select, see SELECT Command in the Developer Guide.

Permission Restrictions

To use COS Select, you must have the permission to cos:GetObject.

• If you are using a root account, you have the permission by default.
• If you are using a sub-account, contact your root account to get the permission to this operation. For more information on permission settings, see Granting a Sub-account Access to COS.

Object Data Format

COS Select supports extracting object data in the following formats:

• CSV: An object is stored in CSV format with its data records separated with a specific delimiter.
• JSON: An object is stored in JSON format, which can be either a JSON file or a JSON list.

• CSV and JSON objects need to be encoded in UTF-8.
• COS Select supports extracting CSV and JSON objects compressed by gzip or bzip2.
• COS Select supports extracting CSV and JSON objects encrypted with SSE-COS.

Request

Sample Request

POST /<ObjectKey>?select&select-type=2 HTTP/1.1
Host: <BucketName-APPID>.cos.<Region>.myqcloud.com
Date: date
Authorization: Auth String

Request body

• Authorization: Auth String (see Request Signature for details).
• The request parameters select and select-type=2 are required, where the former represents the initiation of a select request, and the latter represents the version information of the API.

Request Header

This API uses only a common request header. For more information on common request headers, see Common Request Headers.

Request Body

The following request shows how to initiate a COS Select request to extract all the content of a CSV object and save the result as a CSV object.

<?xml version="1.0" encoding="UTF-8"?>
<SelectRequest>
    <Expression>Select * from COSObject</Expression>
    <ExpressionType>SQL</ExpressionType>
    <InputSerialization>
        <CompressionType>GZIP</CompressionType>
        <CSV>
            <FileHeaderInfo>IGNORE</FileHeaderInfo>
            <RecordDelimiter>\n</RecordDelimiter>
            <FieldDelimiter>,</FieldDelimiter>
            <QuoteCharacter>"</QuoteCharacter>
            <QuoteEscapeCharacter>"</QuoteEscapeCharacter>
            <Comments>#</Comments>
            <AllowQuotedRecordDelimiter>FALSE</AllowQuotedRecordDelimiter>
        </CSV>
    </InputSerialization>
    <OutputSerialization>
        <CSV>
            <QuoteFields>ASNEEDED</QuoteFields>
            <RecordDelimiter>\n</RecordDelimiter>
            <FieldDelimiter>,</FieldDelimiter>
            <QuoteCharacter>"</QuoteCharacter>
            <QuoteEscapeCharacter>"</QuoteEscapeCharacter>
        </CSV>
    </OutputSerialization>
    <RequestProgress>
        <Enabled>FALSE</Enabled>
    </RequestProgress>
</SelectRequest> 

The following request shows how to initiate a COS Select request to extract all the content of a JSON object and save the result as a JSON object.

<?xml version="1.0" encoding="UTF-8"?>
<SelectRequest>
    <Expression>Select * from COSObject</Expression>
    <ExpressionType>SQL</ExpressionType>
    <InputSerialization>
        <CompressionType>GZIP</CompressionType>
        <JSON>
            <Type>DOCUMENT</Type>
        </JSON>
    </InputSerialization>
    <OutputSerialization>
        <JSON>
            <RecordDelimiter>\n</RecordDelimiter>
        </JSON>                                  
    </OutputSerialization>
    <RequestProgress>
        <Enabled>FALSE</Enabled>
    </RequestProgress>                                  
</SelectRequest> 

• The InputSerialization element describes the format of the object to be extracted. It is a required parameter and can be specified in CSV or JSON format.
• The OutputSerialization element describes the format in which the extraction result is saved. This parameter can be specified in CSV or JSON format.
• The format of the object to be extracted can be different from that in which the extraction result is saved, so you can extract an object in JSON format and save the extraction result in CSV format, and vice versa.

The following table shows the composition of the elements in a request body:

Node Name	Parent Node	Description	Type	Required
Expression	SelectRequest	An SQL expression that represents the extraction operation which you need to initiate, such as SELECT s._1 FROM COSObject s. This expression extracts the first column of content from a CSV object. For more information on SQL expressions, see SELECT Command.	String	Yes
ExpressionType	SelectRequest	Expression type, which is an extension. Currently, only SQL expressions and parameters are supported.	String	Yes
InputSerialization	SelectRequest	Describes the format of the object to be extracted	Container	Yes
OutputSerialization	SelectRequest	Describes the output format of the extraction result.	Container	Yes
RequestProgress	SelectRequest	Whether to return the query progress information (QueryProgress). If this parameter is selected, COS Select will periodically return the query progress information.	Container	No

InputSerialization container element

Node Name	Parent Node	Description	Type	Required
CompressionType	InputSerialization	Describes the compression format of the object to be extracted: If the object has not been compressed, this parameter is NONE If the object has been compressed, COS Select currently supports gzip and bzip2 formats. Value range: NONE, GZIP, and BZIP2. Default value: NONE.	String	No
CSV/JSON	InputSerialization	Describes the required file parameters under the corresponding object format. For example, for CSV format, the delimiter needs to be specified.	Container	Yes CSV or JSON

CSV container element (InputSerialization sub-element)

Node Name	Parent Node	Description	Type	Required
RecordDelimiter	CSV	A character that separates the data records in a CSV object into different rows, which is \n by default. You can specify any octal character such as a comma, semicolon, and tab. This parameter supports up to 2 bytes, i.e., you can enter a delimiter in the format of \r\n. Default value: \n.	String	No
FieldDelimiter	CSV	Specifies the character separating rows in a CSV object, which is , by default. You can specify any octal character. This parameter supports up to 1 byte. Default value: ,.	String	No
QuoteCharacter	CSV	If there is a string in the CSV object to be extracted that contains delimiters, you can use QuoteCharacter to escape it so as to prevent it from being cut into several parts. For example, if there is a string "a, b" in the CSV object, double quotation mark " can prevent this string from being separated into two characters (a and b). Default value: ".	String	No
QuoteEscapeCharacter	CSV	If the string to be extracted contains ", then you need to use " to escape it so as to ensure that the string can be escaped normally. For example, your string """ a , b """ will be parsed as " a , b ". Default value: ".	String	No
AllowQuotedRecordDelimiter	CSV	Specifies whether the object to be extracted contains any character that is the same as the delimiter and needs to be escaped using ". When this parameter is set to TRUE, COS Select will escape the character during extraction, which will result in a decrease in the extraction performance. When it is set to FALSE, no escaping will be performed. Default value: FALSE.	Boolean	No
FileHeaderInfo	CSV	Whether the object to be extracted contains a column header. Value range: NONE, USE, IGNORE. NONE indicates that the object contains no column headers, USE indicates that the object contains a column header and you can use the head for extraction (such as SELECT "name" FROM COSObject), and IGNORE indicates that the object contains a column header and you do not intend to use the header for extraction (but you can still use the column index for extraction, such as SELECT s._1 FROM COSObject s).	Enum	No
Comments	CSV	Specifies a record as a comment line. This character is added to the first character of the record. If a record is specified as a comment, COS Select will not perform any analysis on it. Default value: #.	String	No

JSON container element (InputSerialization sub-element)

Node Name	Parent Node	Description	Type	Required
Type	JSON	JSON file type: DOCUMENT indicates that the JSON file contains only an independent JSON object which can be cut into multiple rows LINES indicates that each row in the JSON object contains an independent JSON object Value range: DOCUMENT, LINES	Enum	Yes

OutputSerialization container element

Node Name	Parent Node	Description	Type	Required
CSV /JSON	OutputSerialization	Specifies the output format of the extraction result. Value range: CSV, JSON	Container	Yes, which must be CSV or JSON

CSV container element (OutputSerialization sub-element)

Node Name	Parent Node	Description	Type	Required
QuoteFields	CSV	Specifies whether the output result needs to be escaped with " if it is a file. Value range: ALWAYS, ASNEEDED. ALWAYS indicates applying " to all the output extracted files, and ASNEEDED indicates using it only when needed. Default value: is ASNEEDED.	String	Yes
RecordDelimiter	CSV	A character that separates the data records in the output result into different rows, which is \n by default. You can specify any octal character such as a comma, semicolon, and tab. This parameter supports up to 2 bytes, i.e., you can enter a delimiter in the format of \r\n. Default value: \n.	String	No
FieldDelimiter	CSV	A character that separates each row in the output result into different columns, which is , by default. You can specify any octal character. This parameter supports up to 1 byte. Default value: ,.	String	No
QuoteCharacter	CSV	If there is a string in the output result that contains delimiters, you can use QuoteCharacter to escape it so as to ensure that the string will not be cut in subsequent analysis. For example, if there is a string a, b in the output result, double quotation mark " can prevent this string from being separated into two characters (a and b), and COS Select will convert it to "a , b" to be written to the file. Default value: ".	String	No
QuoteEscapeCharacter	CSV	If the string to be output contains ", then you need to use " to escape it so as to ensure that the string can be escaped normally. For example, your string " a , b" will be converted to """ a , b """ when written to the file. Default value: ".	String	No

JSON container element (OutputSerialization sub-element)

Node Name	Parent Node	Description	Type	Required
RecordDelimiter	JSON	A character that separates the data records in the output result into different rows, which is \n by default. You can specify any octal character such as a comma, semicolon, and tab. This parameter supports up to 2 bytes, i.e., you can enter a delimiter in the format of \r\n. Default value: \n.	String	No

RequestProgress container element

Node Name	Parent Node	Description	Type	Required
Enabled	RequestProgress	Specifies whether COS Select should periodically return the query progress information. Default value: FALSE	Boolean	No

Response

A successful extraction operation will return a 200 OK status code.

Response Header

This API only returns a common response header. For more information, see Common Response Headers.

Response Body

As the size of the response body is unpredictable, COS presents the response body in serialized form, i.e., dividing the response body into multiple parts to be returned. The following shows an overview of the returned response body:

<Message 1>
<Message 2>
<Message 3>
......
<Message n>

Pre-response (Prelude) and Response Result (Data)

COS cuts a extraction result into multiple parts, each of which is a message. Each message consists the pre-response (prelude) and response result (data).

• The prelude consists of two parts:
  • Total length of the message.
  • Total length of all headers.
• The data consists of two parts:
  • Header.
  • Payload.

Both the prelude and data end with a 4-byte CRC code encoded in Big Endian. COS Select uses CRC32 to calculate the CRC code. For more information on CRC32, see the RFC documentation. In addition to data, COS Select additionally spends a total of 16 bytes in transferring the prelude and code.

The integer values in all the messages are transferred in network byte order (i.e., encoded in Big Endian).

The figure below shows what a message and a header consist of. One message may contain multiple headers.

As shown above, each message consists of a prelude, a prelude CRC code (composed of two pieces of information that record the number of bytes), header(s), a payload, and a message CRC code. As can be seen from the above figure, the length of the entire response body is calculated as follows:

Total length of a response body = Length of the prelude + length of the prelude CRC code + length of the payload + length of the header(s) + length of the message CRC code

As the total length of the prelude, the prelude CRC code and the message CRC code is always 16 bytes, the total length of the response body can also be quickly calculated as follows:

Total length of a response body = Length of the payload + length of the header(s) + 16

The following describes the components of the response body in detail:

Component	Description
prelude	Records the total length of each message and the total length of all headers separately. Each record is of 4 bytes, and the total length is 8 bytes: 1. total byte-length: the total length of the message, which is encoded in Big Endian and of 4 bytes in total with the capacity of the record itself included. 2. headers byte-length: the total length of all headers, which is encoded in Big Endian and of 4 bytes in total with the capacity occupied by the record excluded.
prelude CRC	A prelude CRC is encoded in Big Endian and contains a total of 4 bytes. It helps the program quickly determine whether the prelude information is correct so as to reduce blocking during buffering.
header	Metadata of the extraction result recorded by the message, such as data type and body format. The length of this part in bytes varies by data type. A header is stored as a key-value (KV) pair and encoded in UTF-8. The metadata recorded in a header can be displayed in any order, but each metadata entry is recorded only once. Depending on the data type, the following headers may appear in the result returned by COS Select: 1. MessageType Header: This header represent the response type, where the key is ":message-type" and the value can be "error" or "event". "error" indicates that this record is an error message, and "event" indicates that this record is a specific event. 2. EventType Header: This header records the event type, where the key is ":event-type" and the value can be "Records", "Cont", "Progress", "Stats" or "End". "Records" indicates that the event is the returned extraction record, "Cont" the TCP connection hold, "Progress" the periodically returned extraction result, "Stats" the statistics of the query, and "End" the end of query. 3. ErrorCode Header: This header records the error code, where the key is ":error-code" and the value can be an error code listed in Special Error Codes. 4. ErrorMessage Header: This header records the error message, where the key is ":error-message" and the value can be an error message returned by the server, which can be used to locate the error.
Payload	Records the extraction result or official information related to the request.
Message CRC	CRC code encoded in Big Endian containing a total of 4 bytes.

A message may record multiple headers, and each header consists of the following parts:

Component	Description
Header Name Byte-Length	Records the length of the header name in bytes
Header Name	Header type. Value range: ":message-type", ":event-type", ":error-code", ":error-message" ":message-type" indicates that the header records the response type ":event-type" indicates that the header records the event type ":error-code" indicates that the header records the error code " :error-message" indicates that the header records the error message.
Header Value Type	Type of the header value, which is always 7 for COS Select, indicating that the type is String
Value String Byte-Length	Length of the header value in bytes, which is always 2 bytes
Header Value String	Body of the header, i.e., the metadata of the payload, where the length of the header value in bytes depends on the response type

COS Select supports the following response types:

Response Type	Description
Records message	An extraction record message, which can contain a single record, a partial record, or multiple records, depending on the number of extraction results. A response body may contain multiple records messages
Continuation message	A connection continuation message that is sent by COS Select periodically to maintain the TCP connection and appears randomly in the response body. It is recommended to make your client able to automatically identify this type of messages and filter them out so as to avoid smudging the extraction results
Progress message	A progress message returned by COS Select periodically to indicate the current query progress
Stats message	A statistics message about the query returned by COS Select after the query ends
End message	An end message indicating that the query has ended and there is no subsequent response data. The query can be considered to have ended only when a message of this type is received
RequestLevelError message	An error message which will be returned by COS Select when an error occurs during the query process and contains the cause of the error. If COS Select returns this message, it will not return an end message

These response types are as detailed below.

Records Message

• Header format
  A records message contains three types of headers: ":message-type", ":event-type", and ":content-type", as shown below:
  
• Body format
  The body of a records message may contain a single record, a partial record, or multiple records, depending on the number of extraction results.

Continuation Message

• Header format
  A continuation message contains two types of headers: ":message-type" and ":event-type", as shown below:
  
• Body format
  A continuation message contains no body content.

Progress Message

• Header format
  A progress message contains three types of headers: ":message-type", ":event-type", and ":content-type", as shown below:
  
• Body format
  The body of a progress message is XML text which contains the current query progress, mainly including:
  • BytesScanned: If the file is compressed, this value represents the size of the file in bytes before it is decompressed; otherwise, this value represents the size of the file in bytes.
  • BytesProcessed: If the file is compressed, this value represents the size of the file in bytes after it is decompressed; otherwise, this value represents the size of the file in bytes.
  • BytesReturned: Size of the extraction result currently returned by COS Select in bytes.

Below is a sample:

<?xml version="1.0" encoding="UTF-8"?>
<Progress>
     <BytesScanned>512</BytesScanned>
     <BytesProcessed>1024</BytesProcessed>
     <BytesReturned>1024</BytesReturned>
</Progress>

Stats Message

• Header format
  A stats message contains three types of headers: ":message-type", ":event-type", and ":content-type", as shown below:
  
• Body format
  The body of a stats message is XML text which contains the statistics of the current query, mainly including:
  • BytesScanned: If the file is compressed, this value represents the size of the file in bytes before it is decompressed; otherwise, this value represents the size of the file in bytes.
  • BytesProcessed: If the file is compressed, this value represents the size of the file in bytes after it is decompressed; otherwise, this value represents the size of the file in bytes.
  • BytesReturned: Size of the extraction result returned by COS Select in the query in bytes.

Below is a sample:

<?xml version="1.0" encoding="UTF-8"?>
<Stats>
     <BytesScanned>512</BytesScanned>
     <BytesProcessed>1024</BytesProcessed>
     <BytesReturned>1024</BytesReturned>
</Stats>

End Message

• Header format
  An end message contains two types of headers: ":message-type" and ":event-type", as shown below:
  
• Body format
  An end message contains no body content.

Request Level Error Message

• Header format
  A request level error message contains three types of headers: ":error-code", ":error-message", and ":message-type", as shown below:
  

For more information on the error code in a request level error message, see Special Error Codes.

• Body format
  A request level error message contains no body content.

Special Error Codes

For common error messages for this request, see Error Codes. Special error codes are as shown below:

Error Code	Error Message	Meaning	HTTP Status Code
InvalidXML	The XML is invalid	The XML format is invalid.	400 Bad Request
MissingRequiredParameter	The SelectRequest entity is missing a required parameter	A required parameter is missing in the extraction request.	400 Bad Request
MissingExpectedExpression	The SQL expression is missing	An SQL expression is missing.	400 Bad Request
MissingInputSerialization	The input serialization is missing	No data serialization format of the input CSV object is specified.	400 Bad Request
InvalidCompressionFormat	The file is not in a supported compression format. Only GZIP and BZIP2 are supported	The file is in an invalid compression format. Only gzip and bzip2 are supported.	400 Bad Request
MissingInputFormat	The input format is missing	The input format is missing.	400 Bad Request
InvalidFileHeaderInfo	The input FileHeaderInfo is invalid. Only NONE, USE, and IGNORE are supported	The input file header information is invalid. Only NONE, USE, and IGNORE are supported.	400 Bad Request
InvalidRequestParameter	The input RecordDelimiter of CSV is invalid	The record delimiter of the CSV file is invalid.	400 Bad Request
InvalidRequestParameter	The input FieldDelimiter of CSV is invalid	The field delimiter of the CSV file is invalid.	400 Bad Request
InvalidRequestParameter	The input QuoteCharacter of CSV is invalid	The quote character of the CSV file is invalid.	400 Bad Request
InvalidRequestParameter	The input AllowQuoteRecordDelimiter of CSV is invalid. Only TRUE and FALSE are supported	The configuration for enabling the escape character in the input CSV file is invalid. Only TRUE and FALSE are supported.	400 Bad Request
InvalidJsonType	The JsonType is invalid. Only DOCUMENT and LINES are supported	The JSON type is invalid. Only DOCUMENT and LINES are supported.	400 Bad Request
MissingOutputSerialization	The output serialization is missing.	No data serialization format of the output CSV object is specified.	400 Bad Request
MissingOutputFormat	The output format is missing	The output format is missing.	400 Bad Request
InvalidQuoteFields	The QuoteFields is invalid. Only ALWAYS and ASNEEDED are supported	The escaping rule is invalid. Only ALWAYS and ASNEEDED are supported.	400 Bad Request
InvalidRequestParameter	The output RecordDelimiter of CSV is invalid	The record delimiter of the output CSV file is invalid.	400 Bad Request
InvalidRequestParameter	The output FieldDelimiter of CSV is invalid	The field delimiter of the output CSV file is invalid.	400 Bad Request
InvalidRequestParameter	The output QuoteCharacter of CSV is invalid	The escape character of the output CSV file is invalid.	400 Bad Request
InvalidRequestParameter	The output QuoteEscapeCharacter of CSV is invalid	The double quotation mark escape character of the output CSV file is invalid.	400 Bad Request
InvalidRequestParameter	The output RecordDelimiter of JSON is invalid	The record delimiter of the output JSON file is invalid.	400 Bad Request
SQLParsingError	Encountered an error parsing the SQL expression	An error occurred when parsing the SQL expression.	400 Bad Request
SQLParsingError	Other expressions are not allowed in the SELECT list when '*' is used without dot notation.	The SELECT list does not allow '*' to be used without dot notation.	400 Bad Request
SQLParsingError	The SQL expression contains an empty SELECT	The SQL expression contains an empty SELECT clause.	400 Bad Request
SQLParsingError	GROUP is not supported in the SQL expression	The GROUP clause is not supported in the SQL expression.	400 Bad Request
SQLParsingError	UNION is not supported in the SQL expression	The UNION clause is not supported in the SQL expression.	400 Bad Request
SQLParsingError	FROM is missing in the SQL expression	The FROM clause is missing in the SQL expression.	400 Bad Request
SQLParsingError	ORDER is not supported in the SQL expression	The ORDER clause is not supported in the SQL expression.	400 Bad Request
SQLParsingError	The column index is invalid in the SQL expression	The column index specified in the SQL expression is invalid.	400 Bad Request
SQLParsingError	The table alias is invalid in WHERE	The table alias in the WHERE clause is invalid.	400 Bad Request
Bzip2DecompressError	Encountered an error decompressing the bzip2 file	An error occurred when decompressing the bzip2 file.	400 Bad Request
Bzip2DecompressError	BZIP2 is not applicable to the queried object	The bzip2 format is not applicable to decompressing the object to be queried.	400 Bad Request
GzipDecompressError	Encountered an error decompressing the gzip file	An error occurred when decompressing the gzip file.	400 Bad Request
GzipDecompressError	GZIP is not applicable to the queried object	The gzip format is not applicable to decompressing the object to be queried.	400 Bad Request
Busy	The service is busy. Please retry later	The backend service is busy. Please retry later.	400 Bad Request
Overload	The service is overload. Please retry later	The backend service is overloaded. Please retry later.	400 Bad Request
AmbiguousFieldName	Field name matches to multiple fields in the file	The specified header name has multiple identical values.	400 Bad Request
ComparisonFailed	Attempt to compare failed	The attempt to compare failed. Please retry.	400 Bad Request
CastFailed	Attempt to convert from one data type to another using CAST failed in the SQL expression.	The attempt to convert from one data type to another using the CAST function failed in the SQL expression.	400 Bad Request
OverMaxRecordSize	The length of a record in the input or result is greater than maxCharsPerRecord of 1 MB	The size of a record in the input or output exceeds the limit of 1 MB.	400 Bad Request
LastRecordParseFail	Please check the last record in the input	Please check the last record in the input file.	400 Bad Request
CSVParsingError	Encountered an error parsing the CSV file	An error occurred when parsing the CSV file.	400 Bad Request
JSONParsingError	Encountered an error parsing the JSON file	An error occurred when parsing the JSON file.	400 Bad Request
ErrorWritingRow	Encountered an error parsing the SELECT result. Please try again	Unable to format your query result. Please check the file and retry.	400 Bad Request
InvalidRequestParameter	The input Comment of CSV is invalid	The comment of the CSV file is invalid.	400 Bad Request
InvalidTextEncoding	UTF-8 encoding is required. Please check the file and try again.	The file and the result can only be encoded in UTF-8.	400 Bad Request
NoSuchKey	The specified key does not exist	The specified object key does not exist.	404 Not Found
AccessDenied	Access Denied	Access is denied due to incorrect signature or permission.	403 Forbidden
MethodNotAllowed	The specified method is not allowed against this resource	The current resource does not support the HTTP method.	405 Method Not Allowed
InternalError	We encountered an internal error. Please try again	The server encountered an internal error.	500 Internal Server

Samples

Sample 1. Extracting Content from an Object in CSV Format

The following sample shows the process of calling this API to extract all the content from a CSV object and outputting the extraction result in CSV format. The object to be extracted is named exampleobject.csv and stored in the bucket examplebucket-1250000000 in Beijing (ap-beijing).

POST /exampleobject.csv?select&select-type=2 HTTP/1.1
Host: examplebucket-1250000000.cos.ap-beijing.myqcloud.com
Date: Tue, 12 Jan 2019 11:49:52 GMT
Authorization: authorization string
Content-Length: content length

<?xml version="1.0" encoding="UTF-8"?>
<SelectRequest>
    <Expression>Select * from COSObject</Expression>
    <ExpressionType>SQL</ExpressionType>
    <InputSerialization>
        <CompressionType>None</CompressionType>
        <CSV>
            <FileHeaderInfo>IGNORE</FileHeaderInfo>
            <RecordDelimiter>\n</RecordDelimiter>
            <FieldDelimiter>,</FieldDelimiter>
            <QuoteCharacter>"</QuoteCharacter>
            <QuoteEscapeCharacter>"</QuoteEscapeCharacter>
            <Comments>#</Comments>
        </CSV>
    </InputSerialization>
    <OutputSerialization>
        <CSV>
            <QuoteFields>ASNEEDED</QuoteFields>
            <RecordDelimiter>\n</RecordDelimiter>
            <FieldDelimiter>,</FieldDelimiter>
            <QuoteCharacter>"</QuoteCharacter>
            <QuoteEscapeCharacter>"</QuoteEscapeCharacter>
        </CSV>                               
    </OutputSerialization>
</SelectRequest> 

If you need to execute different extraction commands, you can modify the SQL command in the Expression element. For more information on commands, see SELECT Command. Some common extraction scenarios are described below.

• Suppose that you use a column index to filter the content of an object. You can use s._n to filter out the data in the n column, with the minimum value of n being 1. The following command will filter out the records in column 3 with a value greater than 100 from the object and return columns 1 and 2 of those records:

  SELECT s._1, s._2 FROM COSObject s WHERE s._3 > 100

• If your CSV object has a column header and you want to filter the content of the object using the name of the header (by setting FileHeaderInfo to Use), you can use s.name for indexing. The following command will filter out records with a header named Id or FirstName:

  SELECT s.Id, s.FirstName FROM COSObject s

• You can also specify a function in the SQL expression. The following command will count the number of records in the first column that are smaller than 1:

  SELECT count(*) FROM COSObject s WHERE s._1 < 1

The following is a sample response:

HTTP/1.1 200 OK
x-cos-id-2: cos_id_demo
x-cos-request-id: cos_request_id_demo
Date: Tue, 12 Jan 2019 11:50:29 GMT

A series of messages

Sample 2. Extracting Content from an Object in JSON Format

The following sample shows the process of calling this API to extract all the content from a JSON object and outputting the extraction result in CSV format. The object to be extracted is named exampleobject.json and stored in the bucket examplebucket-1250000000 in Beijing (ap-beijing).

POST /exampleobject.json?select&select-type=2 HTTP/1.1
Host: examplebucket-1250000000.cos.ap-beijing.myqcloud.com
Date: Tue, 12 Jan 2019 11:52:29 GMT
Authorization: authorization string
Content-Length: content length

<?xml version="1.0" encoding="UTF-8"?>
<SelectRequest>
    <Expression>Select * from COSObject</Expression>
    <ExpressionType>SQL</ExpressionType>
    <InputSerialization>
        <CompressionType>NONE</CompressionType>
        <JSON>
            <Type>DOCUMENT</Type>
        </JSON>
    </InputSerialization>
    <OutputSerialization>
        <CSV>
            <QuoteFields>ASNEEDED</QuoteFields>
            <RecordDelimiter>\n</RecordDelimiter>
            <FieldDelimiter>,</FieldDelimiter>
            <QuoteCharacter>"</QuoteCharacter>
            <QuoteEscapeCharacter>"</QuoteEscapeCharacter>
        </CSV>                               
    </OutputSerialization>
</SelectRequest> 

Similarly, you can also perform different extraction commands on JSON objects by modifying the SQL command in the Expression element. For more information on commands, see SELECT Command. Some common extraction scenarios are described below.

• You can extract the corresponding data using the JSON attribute name. The following command will filter out records whose city value is Seattle from the object and return the country and city information of those records:

  SELECT s.country, s.city from COSObject s where s.city = 'Seattle'

• You can also specify a function in the SQL expression. The following command will count the total number of records in the JSON object:

  SELECT count(*) FROM COSObject s

Notes

Unlike the GET Object API, SELECT Object Content does not support the following features:

• Returning a part of an object: You cannot use parameters such as Range to specify to return a part of an object.
• Manipulating archived objects (in ARCHIVE storage class). COS Select cannot directly manipulate archived objects. To do so, you need to retrieve the data first.