CREATE EXTERNAL TABLE|V4.2.1|OceanBase Database| docs|Distributed Database

CREATE EXTERNAL TABLE

Last Updated：2026-07-10 03:29:09 Updated

Description

This statement creates a new external table in the database.

An external table is a key feature in a database management system. Generally, a table in a database stores data in the storage space of the database, whereas 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. After that, you can use the external table to read data 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 }
    )
    [ PATTERN = '<regex_pattern>' ]

Parameter description

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 are automatically mapped to the definition columns of the external table in order.
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`.
AS	Manually specifies column mappings. When the order of columns in a file is different from that in the external table, you can specify the correspondence between a column in the external table and the Nth column in the file by using the pseudo-column `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 mappings, automatic mappings become invalid, and you must manually specify mappings for all columns.
LOCATION	The path where the external table is stored. Generally, the data file of an external table is stored in a separate directory, which can contain subdirectories. When you create an external table, the table automatically collects all files in the directory. The local `LOCATION` is specified in the `LOCATION = '[file://] local_file_path'` format, where `local_file_path` can be a relative path or an absolute path. If an absolute path is used, the current directory must be the installation directory of OceanBase Database. `secure_file_priv` specifies the file path that the OBServer node has the permission to access. `local_file_path` must be a subpath of `secure_file_priv`. The remote `LOCATION` is specified in the `LOCATION = '{oss\\|cos}://$ACCESS_ID:$ACCESS_KEY@$HOST/remote_file_path'` format, where `$ACCESS_ID`, `$ACCESS_KEY`, and `$HOST` are the access information required when you access OSS/COS. These sensitive access information are stored in encrypted form 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 in the object storage path 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. Only the CSV format is supported at present. `LINE_DELIMITER`: the line delimiter for a CSV file. The default value is `LINE_DELIMITER='\n'`. `FIELD_DELIMITER`: the field delimiter for a CSV file. The default value is `FIELD_DELIMITER='\t'`. `ESCAPE`: the escape character for a CSV file. It can be only 1 byte in length. The default value is `ESCAPE ='\'`. `FIELD_OPTIONALLY_ENCLOSED_BY`: the characters that enclose field values in a CSV file. 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 sets. If this parameter is not specified, the default value UTF8MB4 takes effect. `NULL_IF`: the string to be treated as `NULL`. The default value is an empty string. `SKIP_HEADER`: specifies to skip the file header and indicates the number of lines to be skipped. `SKIP_BLANK_LINES`: specifies whether to skip blank lines. The default value is `FALSE`, which indicates that blank lines are not skipped. `TRIM_SPACE`: specifies whether to remove leading and trailing spaces from fields. The default value is `FALSE`, which indicates that leading and trailing spaces in fields are not removed. `EMPTY_FIELD_AS_NULL`: specifies whether to treat an empty string as `NULL`. The default value is `FALSE`, which indicates that an empty string is not treated as `NULL`.
PATTERN	A regular expression pattern for filtering files in the `LOCATION` directory. For each file in the `LOCATION` directory, if the file path matches the pattern, the external table accesses the file. Otherwise, the external table skips the file. If this parameter is not specified, the external table, by default, accesses all files in the `LOCATION` directory. The external table stores the list of files that match the `LOCATION` directory and the `PATTERN` in the system tables of the database. When the external table is scanned, it accesses external files based on this list.

Usage

If an external file is deleted, files in the file list of the external table will no longer exist. In this case, the external table ignores the non-existent files.
If an external file is modified, the external table accesses the latest data of the external file. If the modification of an external file is concurrent with a query on the external table, the result of the query may be unexpected. Therefore, avoid modifying external files while querying the external table.
If a new file is added to an external directory, the external table does not access the new file. To add the new file to the file list of the external table, execute an operation to update the external table's file list.

Examples

Prepare data. First, set the path of secure_file_priv to /home/admin/. Place the CSV file extdata.csv, which corresponds to the data of the external table 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

Since secure_file_priv is a GLOBAL variable, you must execute \q 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 data in 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

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