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. Data of an internal table is stored in the storage space of the database, while data of an external table is 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 data from the data file by using the external table. 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.
column_type	The data 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 pseudo-column `metadata$filecol{N}` to specify the mappings between the Nth column in the file and the columns in the external table. For example, `c2 INT AS (metadata$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 need to manually define 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'`, where `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 OBServer nodes are granted access to. `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@$HOST/remote_file_path'`, where `$ACCESS_ID`, `$ACCESS_KEY`, and `$HOST` are required for accessing OSS or COS. These sensitive access information will be stored in the system tables of the database in an encrypted form. Notice When you use object storage service paths, separate the parameters in the object storage service path with `&`. Make sure that the characters in the value of each parameter are uppercase or lowercase letters, digits, or `/-_$+=`. If the value contains other characters, 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 used by the file. For more information about the character sets supported in Oracle mode, see Character set and collation. The default character set is UTF8MB4 if you do not specify one. `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 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. By default, if this parameter is not specified, all files in the directory specified by `LOCATION` are accessible to the external table. The system table of the database stores the list of files that match the `LOCATION` parameter and are specified by the `PATTERN` parameter. The external table accesses external files based on this list during a scan.
PARTITION_TYPE = USER_SPECIFIED	Specify `PARTITION_TYPE = USER_SPECIFIED` when 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 meet the expectation. Therefore, you need to avoid modifying the external file while querying the external table.
The external table only accesses the files 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

Prepare data. First, set the path of secure_file_priv to /home/admin/. 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 to which you are 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 command to 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 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