CREATE EXTERNAL TABLE|V4.3.0| docs|Distributed Database

CREATE EXTERNAL TABLE

Last Updated：2025-12-02 02:51:29 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 need to 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 Data Manipulation Language (DML) operations on it. You cannot define constraints or create indexes on external tables.

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 }
    )
    [ PATTERN = '<regex_pattern>' ]

Parameters

Parameter	Description
table_name	The name of the external table to be created.
column_name	The name of a column of the external table. By default, the data columns in the file and the columns of the external table are automatically matched in sequence.
column_type	The data type of a column of the external table. You cannot define constraints such as `DEFAULT`, `NOT NULL`, `UNIQUE`, `CHECK`, `PRIMARY KEY`, or `FOREIGN KEY` for the external table columns.
AS	Manually specifies column mapping. If the sequence of columns in the file does not match that in the external table, you can specify the correspondence between a column of the external table and the Nth column in the file by using a pseudocolumn that is represented by `metadata$filecol{N}`. For example, `c2 INT AS (metadata$filecol4)` indicates that the `c2` column in the external table corresponds to the fourth column in the file. Note that if you specify manual column mapping, automatic mapping relationships become invalid, and you must define mappings for all columns manually.
LOCATION	The path where the external table files are stored. Generally, the data files of an external table are 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'`. Here, `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. The `secure_file_priv` parameter specifies the path that OBServer nodes are granted access to. `local_file_path` must be a subdirectory of the path specified by the `secure_file_priv` parameter. The remote `LOCATION` parameter is specified in the format of `LOCATION = '{oss\\|cos}://$ACCESS_ID:$ACCESS_KEY@$HOST/remote_file_path'`. Here, `$ACCESS_ID`, `$ACCESS_KEY`, and `$HOST` are required for accessing Object Storage Service (OSS) or Cloud Object Storage (COS). These sensitive access information is encrypted and stored in the system tables of the database. Notice When you use object storage paths, separate the parameters in the object storage path with `&`. Make sure that the characters in the value of each parameter of the object storage path are uppercase or lowercase letters, digits, characters from the `/-_$+=` set, or wildcard characters. If you enter characters other than the aforesaid ones, the setting may fail.
FORMAT	Specifies the format of external files. `TYPE`: the type of external files. At present, 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 files. For more information about character sets supported in MySQL mode, see Character set. The default character set is UTF8MB4 in MySQL mode of OceanBase Database. `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 files. The default value is `FALSE`, which specifies not to remove leading and trailing spaces from fields in files. `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 `LOCATION` directory. 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. By default, if this parameter is not specified, all files in the directory specified by `LOCATION` are accessible to the external table. The external table stores the list of files that match the `LOCATION` parameter value in the system tables of the database. During a scan, the external table accesses external files based on this list.

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 querying the external table.
The external table accesses only the files listed in the file list when new files are added to the external directory. If you want 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 current locally connected OBServer node.

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 CSV file contains the following data:
```
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