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    Importing and Exporting COS Data at High Speed with External Table

    Last updated: 2024-02-02 15:27:57
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      Querying COS Data with COS_EXT

      COS_EXT is an external data access extension for accessing COS files. By defining an external table through DDL, you can run DML in the external table as a normal data table to manipulate COS data. The following are supported currently:
      Read COS data as an external table.
      Export results to COS as an external table.
      Perform simple analysis of COS data as an external table.

      Notes

      1. Only files in text formats such as CSV and GZIP compressed format files are supported.
      2. Only COS data in the same region can be read. For example, a cluster in Guangzhou Zone 4 can only read COS data in the Guangzhou region.
      3. Only your own COS data can be read by your cluster.
      4. Write-only external tables can only be used for the INSERT statement but not UPDATE, DELETE, and SELECT statements.
      5. Deleting an external table will not delete the corresponding data in COS.

      Directions

      1. Define the COS_EXT extension.
      Note:
      The scope of the COS external table extension is the database.
      The creation command is as follows:
      CREATE EXTENSION IF NOT EXISTS cos_ext SCHEMA public;
      The deletion command is as follows:
      DROP EXTENSION IF EXISTS cos_ext;
      2. Define the COS external table. For syntax, see Syntax description.
      3. Manipulate data in the COS external table.

      Syntax description

      Definite the read-only input table
       CREATE [READABLE] EXTERNAL TABLE tablename
       ( columnname datatype [, ...] | LIKE othertable )
       LOCATION (cos_ext_params)
       FORMAT 'TEXT'
             [( [HEADER]
                    [DELIMITER [AS] 'delimiter' | 'OFF']
                    [NULL [AS] 'null string']
                    [ESCAPE [AS] 'escape' | 'OFF']
                    [NEWLINE [ AS ] 'LF' | 'CR' | 'CRLF']
                    [FILL MISSING FIELDS] )]
            | 'CSV'
             [( [HEADER]
                    [QUOTE [AS] 'quote']
                    [DELIMITER [AS] 'delimiter']
                    [NULL [AS] 'null string']
                    [FORCE NOT NULL column [, ...]]
                    [ESCAPE [AS] 'escape']
                    [NEWLINE [ AS ] 'LF' | 'CR' | 'CRLF']
                    [FILL MISSING FIELDS] )]
       [ ENCODING 'encoding' ]
       [ [LOG ERRORS [INTO error_table]] SEGMENT REJECT LIMIT count
              [ROWS | PERCENT] ]
      Define the write-only output table
       CREATE WRITABLE EXTERNAL TABLE table_name
       ( column_name data_type [, ...] | LIKE other_table )
       LOCATION (cos_ext_params)
       FORMAT 'TEXT'
                [( [DELIMITER [AS] 'delimiter']
                [NULL [AS] 'null string']
                [ESCAPE [AS] 'escape' | 'OFF'] )]
            | 'CSV'
                [([QUOTE [AS] 'quote']
                [DELIMITER [AS] 'delimiter']
                [NULL [AS] 'null string']
                [FORCE QUOTE column [, ...] ]
                [ESCAPE [AS] 'escape'] )]
       [ ENCODING 'encoding' ]
       [ DISTRIBUTED BY (column, [ ... ] ) | DISTRIBUTED RANDOMLY ]
      1. cos_ext_params description
      cos://cos_endpoint/bucket/prefix secretId=id secretKey=key compressType=[none|gzip] https=[true|false]

      Parameter description

      Parameter
      Format
      Required
      Description
      URL
      COS V4: cos://cos.{REGION}.myqcloud.com/{BUCKET}/{PREFIX}
      COS V5: cos:// {BUCKET}-{APPID}.cos.{REGION}.myqcloud.com/{PREFIX}
      Yes
      secretId
      None
      Yes
      Secret ID used for API access. See API Key Management
      secretKey
      None
      Yes
      Secret key used for API access. See API Key Management
      HTTPS
      true Ι false
      No
      Whether to use HTTPS to access COS. Default value: true
      compressType
      gzip
      No
      Whether to compress COS files. Default value: empty (not to compress)

      URL parameter description

      REGION: Region supported by COS, which needs to be the same region as the instance. For valid values, see Regions and Access Endpoints.
      BUCKET: COS bucket name, which can be seen in COS Bucket List. The name here does not contain the APPID. If you see the bucket name test-123123123 in the list, just enter "test".
      PREFIX: COS object name prefix, which can be empty and include multiple "/".
      In a read-only table scenario, prefix specifies the name prefix of the object to be read. If prefix is empty, all files in the bucket will be read; if it ends with "/", all files in the folder and subfolders will be matched; otherwise, all files in the folder and subfolders matched by prefix will be read. For example, COS objects include read-bucket/simple/a.csv, read-bucket/simple/b.csv, read-bucket/simple/dir/c.csv, and read-bucket/simple_prefix/d.csv.
      If prefix is specified as simple, all files will be read, including simple_prefix with the matching directory name prefix. The following is the list of objects: read-bucket/simple/a.csv read-bucket/simple/b.csv read-bucket/simple/dir/c.csv read-bucket/simple_prefix/d.csv
      If prefix is specified as simple/, all files including simple/ will be read, including: read-bucket/simple/a.csv read-bucket/simple/b.csv read-bucket/simple/dir/c.csv
      In a write-only table scenario, prefix specifies the output file prefix. If no prefix is specified, files will be written to the bucket. If prefix ends with "/", files will be written to the directory specified by prefix; otherwise, files will be prefixed with the given prefix. For example, if the files that need to be created include a.csv, b.csv, and c.csv, then:
      If prefix is specified as simple/, the following objects will be generated: read-bucket/simple/a.csv read-bucket/simple/b.csv read-bucket/simple/b.csv
      If prefix is specified as simple\\_, the following objects will be generated: read-bucket/simple_a.csv read-bucket/simple_b.csv read-bucket/simple_b.csv

      Use Cases

      Importing COS data

      1. Define the COS extension. 
      CREATE EXTENSION IF NOT EXISTS cos_ext SCHEMA public;
      2. Define a COS read-only external table and a local table. Local table:
      CREATE TABLE cos_local_tbl (c1 int, c2 text, c3 int)
      DISTRIBUTED BY (c1);
      COS external table: Specifies to read all files in simple-bucket in Guangzhou.
      CREATE READABLE EXTERNAL TABLE cos_tbl (c1 int, c2 text, c3 int)
      LOCATION('cos://cos.ap-guangzhou.myqcloud.com/simple-bucket/from_cos/ secretKey=xxx secretId=xxx')
      FORMAT 'csv';
      3. Prepare local table data. Upload the file to the from_cos directory in simple-bucket with the following content:
      1,simple line 1,1
      2,simple line 1,1
      3,simple line 1,1
      4,simple line 1,1
      5,simple line 1,1
      6,simple line 2,1
      7,simple line 2,1
      8,simple line 2,1
      9,simple line 2,1
      Note:
      The imported data does not contain field rows of the table header.
      4. Import COS data.
      INSERT INTO cos_local_tbl SELECT * FROM cos_tbl;
      5. Check the result to see whether the data is consistent.
      SELECT count(1) FROM cos_local_tbl;
      SELECT count(1) FROM cos_tbl;

      Exporting data to COS

      1. Define the COS extension.
      CREATE EXTENSION IF NOT EXISTS cos_ext SCHEMA public;
      2. Define a COS write-only external table. Local table:
      CREATE TABLE cos_local_tbl (c1 int, c2 text, c3 int)
      DISTRIBUTED BY (c1);
      COS external table: Specifies to write all files in simple-bucket in Guangzhou.
      CREATE WRITABLE EXTERNAL TABLE cos_tbl_wr (c1 int, c2 text, c3 int)
      LOCATION('cos://cos.ap-guangzhou.myqcloud.com/simple-bucket/to-cos/ secretKey=xxx secretId=xxx')
      FORMAT 'csv';
      3. Construct the test data.
      insert into cos_local_tbl values
      (1, 'simple line 1' , 1),
      (2, 'simple line 2', 2), 
      (3, 'simple line 3', 3) ,
      (4, 'simple line 4', 4) , 
      (5, 'simple line 5', 5) ,
      (6, 'simple line 6', 6) , 
      (7, 'simple line 7', 7) , 
      (8, 'simple line 8', 8) , 
      (9, 'simple line 9', 9);
      4. Export the data to COS.
      INSERT INTO cos_tbl_wr SELECT * FROM cos_local_tbl;
      5. Check the result.
      
      

      Simple analysis of COS data

      Note:
      When using COS external tables for query analysis without query optimization, we recommend you first import the data locally for complex queries.
      1. Define the COS extension.
      CREATE EXTENSION IF NOT EXISTS cos_ext SCHEMA public;
      2. Prepare the data. Upload the file to the for-dml directory in simple-bucket with the following content:
      1,simple line 1,1
      2,simple line 1,1
      3,simple line 1,1
      4,simple line 1,1
      5,simple line 1,1
      6,simple line 2,1
      7,simple line 2,1
      8,simple line 2,1
      9,simple line 2,1
      3. Define a COS read-only external table.
      CREATE READABLE EXTERNAL TABLE cos_tbl_dml (c1 int, c2 text, c3 int)
      LOCATION('cos://cos.ap-guangzhou.myqcloud.com/simple-bucket/for-dml/ secretKey=xxx secretId=xxx')
      FORMAT 'csv';
      4. Analyze the data in the COS external table.
      SELECT c2, sum(c1) FROM cos_tbl GROUP BY c2;
      
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