CREATE EXTERNAL TABLE|V4.3.1| docs|Distributed Database

CREATE EXTERNAL TABLE

Last Updated：2025-12-03 06:58:03 Updated

Description

This statement creates an external table in a database.

External tables are a key feature in a database management system. Generally, the data of a table in a database is stored in the storage space of the database, while an external table has data stored in an external storage service.

When you create an external table, you must specify the file path and file format of the data. Then, you can read the data of the external table from the external storage service. An external table is read-only. You can use it in a query statement, but you cannot perform DML operations on it. You cannot define constraints or create indexes on an external table.

Syntax

CREATE EXTERNAL TABLE <table_name>
    ( [ <column_name> <column_type> [AS <expr>] ]
      [ , <column_name> <column_type> [AS <expr>] ]
      [ , ... ] )
    LOCATION = '<string>'
    FORMAT = (
      TYPE = 'CSV'
      LINE_DELIMITER = '<string>' | <expr>
      FIELD_DELIMITER = '<string>' | <expr>
      ESCAPE = '<character>' | <expr>
      FIELD_OPTIONALLY_ENCLOSED_BY = '<character>' | <expr>
      ENCODING = 'charset'
      NULL_IF = ('<string>' | <expr>, '<string>' | <expr> ...)
      SKIP_HEADER = <int>
      SKIP_BLANK_LINES = { TRUE | FALSE }
      TRIM_SPACE = { TRUE | FALSE }
      EMPTY_FIELD_AS_NULL = { TRUE | FALSE }
    )
    [ PARTITION BY ( <column_name> [, <column_name> ... ] ) ]
    [ PARTITION_TYPE = USER_SPECIFIED ]
    [ PATTERN = '<regex_pattern>' ]

Parameters

Parameter	Description
table_name	The name of the external table to be created.
column_name	The name of the column in the external table. By default, the data columns in the file are automatically mapped to the columns defined in the external table in sequence.
column_type	The type of the column in the external table. You cannot define constraints such as `DEFAULT`, `NOT NULL`, `UNIQUE`, `CHECK`, `PRIMARY KEY`, or `FOREIGN KEY` for the column.
AS	Manually specifies the mappings between columns. If the order of columns in the file does not match that in the external table, you can use the metadata$filecol{N} pseudo-column to specify the mappings between the Nth column in the file and the columns in the external table. For example, `c2 INT AS (metadata$filecol4)` indicates that the c2 column in the external table corresponds to the fourth column in the file. Note that if you manually specify column mappings, automatic mappings will become invalid, and you must manually specify mappings for all columns.
LOCATION	The path where the external table is stored. Generally, the data of an external table is stored in a separate directory, which can contain subdirectories. When you create an external table, the system automatically collects all files in the specified directory. The local `LOCATION` parameter is specified in the format of `LOCATION = '[file://] local_file_path'`. `local_file_path` can be a relative path or an absolute path. If you specify a relative path, the current directory must be the installation directory of OceanBase Database. `secure_file_priv` specifies the file path that an OBServer node has the permission to access. `local_file_path` must be a subdirectory of `secure_file_priv`. The remote `LOCATION` parameter is specified in the format of `LOCATION = '{oss\\|cos}://$ACCESS_ID:$ACCESS_KEY@$HOST/remote_file_path'`. When you access Object Storage Service (OSS) or Cloud Object Storage (COS), you must specify the access information, such as `$ACCESS_ID`, `$ACCESS_KEY`, and `$HOST`. These sensitive access information will be encrypted and stored in the system tables of the database. Notice When you use an object storage path, separate the parameters in the object storage path with `&`. Make sure that the characters in the value of each parameter are uppercase or lowercase letters, digits, or `/-_$+=`. If you enter characters other than the preceding ones, the setting may fail.
FORMAT	The format of the external file. `TYPE`: the type of the external file. Currently, only CSV files are supported. `LINE_DELIMITER`: the line delimiter for CSV files. The default value is `LINE_DELIMITER='\n'`. `FIELD_DELIMITER`: the field delimiter for CSV files. The default value is `FIELD_DELIMITER='\t'`. `ESCAPE`: the escape character for CSV files. It can only be 1 byte in length. The default value is `ESCAPE ='\'`. `FIELD_OPTIONALLY_ENCLOSED_BY`: the characters that enclose the field values in CSV files. The default value is an empty string. `ENCODING`: the character set encoding format of the file. For more information about the character sets supported in MySQL mode, see Character set. If no character set is specified, the default value UTF8MB4 takes effect. `NULL_IF`: the strings that are to be treated as `NULL` values. The default value is an empty string. `SKIP_HEADER`: specifies to skip the file header, and specifies the number of lines to skip. `SKIP_BLANK_LINES`: specifies whether to skip blank lines. The default value is `FALSE`, which specifies not to skip blank lines. `TRIM_SPACE`: specifies whether to remove leading and trailing spaces from fields in the file. The default value is `FALSE`, which specifies not to remove leading and trailing spaces from fields in the file. `EMPTY_FIELD_AS_NULL`: specifies whether to treat empty strings as `NULL` values. The default value is `FALSE`, which specifies not to treat empty strings as `NULL` values.
PATTERN	A regular pattern string that is used to filter files in the directory specified by `LOCATION`. For each file in the directory specified by `LOCATION`, if the file path matches the pattern string, the external table accesses the file. Otherwise, the external table skips the file. If this parameter is not specified, the external table will access all files in the directory specified by `LOCATION` by default. The system table of the database stores the list of files that match the `LOCATION` parameter and the `PATTERN` parameter. The external table scans files based on this list during access.
PARTITION_TYPE = USER_SPECIFIED	Specify `PARTITION_TYPE = USER_SPECIFIED` if you want to manually add and drop partitions instead of letting the external table automatically manage partitions.

Usage notes

If an external file is deleted, the file no longer exists in the file list when you access the file list. In this case, the external table ignores the missing file.
If an external file is modified, the external table accesses the latest data of the external file. If the modification of the external file conflicts with the query of the external table, the result of the query may not be as expected. Therefore, avoid modifying the external file while the external table is being queried.
The external table only accesses the files listed in the file list when new files are added to the external directory. To add new files to the file list of the external table, you need to update the file list of the external table.

Examples

Set the path of secure_file_priv to /home/admin/, and place the extdata.csv file, which corresponds to the external table data to be imported, in the /home/admin/test directory on the local OBServer node that is connected.

Here is an example of setting the global secure path.
```
obclient> SET GLOBAL secure_file_priv = ""
Query OK, 0 rows affected
obclinet> \q
Bye
```
Note

After you set the secure_file_priv variable, you must execute the \q statement to quit and make the setting take effect.

The content of the CSV file is as follows:
```
1,'Dave','Smith','dsmith@outlook.com','friend',32
2,'Xena','Johnson','xjonson@outlook.com','contact',45
3,'Fred','Jackon','fjackson@outlook.com','co-worker',19
4,'Alma','Tyler','atyler@outlook.com','friend',53
```

obclient> CREATE EXTERNAL TABLE contacts (
    id    INT,
    firstname  VARCHAR(100),
    lastname   VARCHAR(100),
    email      VARCHAR(255),
    category   CHAR(30),
    age        NUMBER
   )
   LOCATION = '/home/admin/test'
   FORMAT = (
     TYPE = 'CSV'
     FIELD_DELIMITER = ','
     FIELD_OPTIONALLY_ENCLOSED_BY ='\''
    )
  PATTERN = 'extdata.csv';

Query data from the contacts external table.

obclient> SELECT * FROM contacts;
+----+-----------+----------+----------------------+-----------+------+
| id | firstname | lastname | email                | category  | age  |
+----+-----------+----------+----------------------+-----------+------+
|  1 | Dave      | Smith    | dsmith@outlook.com   | friend    |   32 |
|  2 | Xena      | Johnson  | xjonson@outlook.com  | contact   |   45 |
|  3 | Fred      | Jackon   | fjackson@outlook.com | co-worker |   19 |
|  4 | Alma      | Tyler    | atyler@outlook.com   | friend    |   53 |
+----+-----------+----------+----------------------+-----------+------+
4 rows in set

References

Create an external table

Manage external files

Update the file list of an external table