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Stage Table Function

Databend supports using standard SQL to query data files located in an internal stage or named external stage.

The schema is automatically detected, same as infer_schema.

Syntax​

SELECT <columns> FROM
{@<stage_name>[/<path>] | '<uri>'} [(
  [ PARTTERN => '<regex_pattern>']
  [ FILE_FORMAT => '<format_name>']
  [ FILES => ( 'file_name' [ , 'file_name' ... ] ) ]
  [ ENDPOINT_URL => <'url'> ]
  [ AWS_KEY_ID => <'aws_key_id'> ]
  [ AWS_KEY_SECRET => <'aws_key_secret'> ]
  [ ACCESS_KEY_ID => <'access_key_id'> ]
  [ ACCESS_KEY_SECRET => <'access_key_secret'> ]
  [ SECRET_ACCESS_KEY => <'secret_access_key'> ]
  [ SESSION_TOKEN => <'session_token'> ]
  [ REGION => <'region'> ]
  [ ENABLE_VIRTUAL_HOST_STYLE => true|false ]
)]

The function parameters are as follows:

FILE_FORMAT = '<format_name>'​

<format_name> should be one of the following:

  1. A built-in file format (see Input & Output File Formats.
  2. A named file format created by CREATE FILE FORMAT.

If not specified for named stages, the format of the stage should be used.

警告

Only parquet file format is currently supported.

PATTERN = '<regex_pattern>'​

A PCRE2-based regular expression pattern string, enclosed in single quotes, specifying the file names to match. Click here to see an example. For PCRE2 syntax, see http://www.pcre.org/current/doc/html/pcre2syntax.html.

FILES = ( 'file1' [ , 'file2' ... ] )​

Specifies a list of one or more files names (separated by commas) to be read.

Connection Options for <uri> only​

These include:

  • ENDPOINT_URL
  • AWS_KEY_ID
  • AWS_SECRET_KEY
  • ACCESS_KEY_ID
  • ACCESS_KEY_SECRET
  • SECRET_ACCESS_KEY
  • SESSION_TOKEN
  • REGION
  • ENABLE_VIRTUAL_HOST_STYLE

They are explained Create Stage.

Query Examples​

Select from Named Stage​

-- New stage.
create stage lake;
    
-- Stage the data file into internal stage.
copy into @lake from (select * from numbers(10)) file_format = (type = PARQUET);

-- Show files in the internal stage.
list @lake;
+-------------------------------------------------------+------+------------------------------------+-------------------------------+---------+
| name                                                  | size | md5                                | last_modified                 | creator |
+-------------------------------------------------------+------+------------------------------------+-------------------------------+---------+
| data_8f414f66-5a94-42ad-ad52-a9076541799e_0_0.parquet |  258 | "7DCC9FFE04EA1F6882AED2CF9640D3D4" | 2023-02-24 09:55:46.000 +0000 | NULL    |
+-------------------------------------------------------+------+------------------------------------+-------------------------------+---------+

-- Query.
select min(number), max(number) from @lake (pattern => '.*parquet');

+-------------+-------------+
| min(number) | max(number) |
+-------------+-------------+
|           0 |           9 |
+-------------+-------------+

Select from URI​

file_format must be specified.

select *  from 's3://bucket/test.parquet' 
( access_key_id => 'your-access-key-id', 
  secret_access_key => 'your-secret-access-key',
  endpoint_url => 'your-object-storage-endpoint',
  file_format => 'parquet');